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The Green Bodies of the Intestinal Wall of Certain Chaetopteridae. by C

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The Green Bodies of the Intestinal Wall of Certain Chaetopteridae. by C The Green Bodies of the Intestinal Wall of certain Chaetopteridae. By C. Berkeley. With Plate 26. INTRODUCTION. CLAPAREDB (1) seems to have been the first to attribute the colour of the intestinal wall of Chaetopterus variopeda- t u s Eenier to the presence of small spherical green granules in the epithelial cells of the tissue. The distribution of the granules in the cells was subsequently described by Laffuie (2) and by Lankester (3). These three authors considered that they con- sisted of a pigmented cell secretion concerned in one way or another with digestion. Brandes (4), on the other hand, expressed the view that the granules were not to be looked upon as a metabolic product of the worm, but were organisms of an algal nature analogous to those which had previously been described living symbiotically or parasitically in various animals by Brandt (5) and others. He based this view on the general appearance of the granules as figured by Lankester and on the similarity between the absorption spectrum of the green pigment chaetopterin extracted from them and that of chlorophyll. Enders (6), commenting on this difference of view, suggests that, if Brandes is correct, it should be possible to cultivate the green organism outside the worm as I'amintzin (7) and Beijerinck (8) did in the case of Zoochlorella from Hydra viridis. Since that time many instances of algal and animal associa- tions have been recorded, but no conclusive evidence appears to have been brought forward in the case of Chaetopterus. 466 C. BERKELEY The common occurrence of three species of Chaetopteridae, each representing a different genus of the family, in the im- mediate vicinity of the Biological Station, Nanaimo, B.C., in each of which the intestinal tract is visible through the body- wall of the abdominal region as a well-defined deep green tract, suggested that some information on the nature of the pigmented bodies in the epithelial cells might be obtained by a comparative study. The three species are : (1) Mesochaetopterus taylori Potts; (2) Phyllochaetopter us prolifioa Potts ; and (3) Leptochaetopterus pottsi Berkeley. They have all been recorded, and the first two described, by Potts (9) ; the third, only briefly mentioned by him and attributed to the genus Telepsavus, was described more fully by my wife (10). Mesochaetopterus and Leptochaetopterus inhabit tubes which run a considerable distance into the sand-banks in which they are found, the former frequently two feet or more in an almost vertical direction and then as far in a more horizontal one, the latter about half these distances. In neither case does the posterior end of the tube emerge to the surface as in that of Chaetopterus variopedatus. The animals are usually at least half the length of their tubes, and the abdominal region makes up by far the greatest part of their length. Phyllochae- topterus is found in tubes occurring in matted masses on gravelly bottoms at a depth of 15 to 20 fathoms, and is obtained easily in the dredge. Potts points out that it has the interesting faculty of increasing asexually, posterior portions of individuals splitting off and regenerating the anterior regions. He did not observe the sexual forms, but these are occasionally found. Preliminary examination showed that the green coloration of the intestinal wall was due in all three cases to spherical granules very similar to those described by Lankester from Chaetopterus variopedatus. A pigment having the pro- perties of chaetopterin could be extracted from each of them. It is easily soluble in strong hydrochloric acid (50 per cent. ' pure ' HC1), in which it seems to be quite stable even on prolonged boiling, differing thus very essentially from chlorophyll. No GREEN BODIES OF CHAETOPTERIDAE 467 phaecocyanin, or other water-soluble pigment, could be extracted from the green tissue. The tissue from each of the three species was examined by means of sections and the green bodies from teased-out material by hanging drops and dry films. SECTIONS. The green colour of the intestinal wall remains permanent in material fixed in sublimate and bichromate (Zenker's mixture) or picro-formol (Bouin). In transverse sections of the abdominal region of Mesochaetopterus or Leptochaetopterus thus fixed the intestinal wall is seen at low magnification to con- sist of a heavily pigmented, much convoluted, tissue. The intes- tine occupies a larger part of the abdominal cavity than in Chaetopterus variopedatus, and the lumen is much smaller in relation to the thickness of the wall (fig. 1, PI. 26). Much the same condition exists in Phyllochaetopterus, but in this case the intestinal wall is relatively thinner and less convoluted and the lumen larger. At higher magnification the intestinal wall is seen to be built up of the usual two layers of cells, the columnar tissue being similar to that figured by Lankester and others for Chaeto- pterus variopedatus. In sections taken anywhere except near the anal end the cells of this tissue are crowded with spheri- cal green bodies varying in diameter from 1 to 8/x (fig. 2, PL 26). In Mesochaetopterus they are usually an olive shade, but some variation occurs in the depth of colour. In Leptochae- topterus it is commonly lighter and more blue-green. In both these species the green bodies are as a rule quite homogeneous and no structure can be brought out by staining. Quite rarely a few individuals have been seen in the sections showing a granular structure. A circular area rather more refractive than its sur- roundings, seen in some of the smaller and more lightly coloured green bodies, was at first taken for a nucleus, but it could not be differently stained. I shall refer to this later. In Phyllochae- topterus there is more variation in the colour of the green bodies than in either of the other species, some of them approxi- 468 C. BERKELEY mating to a blue colour, and a considerable number of them show distinct granular structure (fig. 3, PI. 26). The granules are accentuated in sections stained with both nuclear and cyto- plasmic stains. In addition to the more or less uniformly dis- tributed granules a roughly circular area staining selectively with haematoxylin occurs in some of the green bodies and may be a nucleus. In sections taken near the anal end of the annelids a different condition is found. Here the green bodies are uniformly smaller than in the more anterior region of the abdomen, averaging no more than 2/x in diameter and are not distributed throughout the epithelial cells. The majority are concentrated at the ends which border on the lumen, but a few are found scattered through the cells, usually lying immediately adjacent to the cell-wall (fig. 4, PL 26). The nearer the anal end the section is taken the fewer are the green bodies in the cells, until, finally, they are entirely absent from the last few segments. In the course of his studies of the development of C h a e t o - pterus variopedatus, Enders found that the green colour of the digestive tract could be observed in the larvae at an early stage, and that by the time they had attained a length of 2 mm. it had become quite marked, though less so than in fully trans- formed larvae. Free-swimming chaetopterid larvae of about this length have been taken over the beds in which Mesochaeto- pterus and Leptochaetopterus occur, and probably belong to one or other of these species. In these larvae the colour of the digestive tract was quite apparent and sections showed that it was due to green bodies in the epithelial cells precisely similar to those found in the adults. The conditions of size and of density of distribution in the cells resembled those found in sections taken near the posterior end of the adult animals. In material fixed in acid alcoholic fixatives the pigment is entirely removed from the green bodies. A fixative consisting of 95 per cent, methyl alcohol (100 parts), water (20 parts), formalin (5 parts), and glacial acetic acid (5 parts) was used for this purpose. Pieces of abdomen of Mesochaetopterus left in this fixative until decolorization was complete (some GREEN BODIES OF CHAETOPTERIDAE 469 months) were stained in bulk in borax-carmine. Sections showed stained, but shrunken and deformed, residues of the formerly green bodies in the epithelial cells. More satisfactory results were obtained by fixing for a short period in the alcoholic fixative and completing the decolorization, in the sections, with alcohol containing hydrochloric acid (10 drops cone. HC1 to 100 cc. 95 per cent, alcohol). In sections so treated the green bodies were much less deformed. They could be stained with any of the ordinary cytoplasmic stains. Lankester mentions a ' colourless stroma ' which remains after the green bodies in Chaetopterus variopedatus have had their pigment removed, and this corresponds without doubt with the de- colorized residuum in my sections. The fact that such a stain- able residuum remained after decolorization seemed to indicate that the green bodies had something of the nature of a bounding membrane or cell-wall, and to be opposed to the view that they consisted of a cell secretion. Sections of material fixed in osmic acid fixatives showed that the green bodies contain a quantity of oil. They are stained intensely black, whilst the remainder of the contents of the epithelial cells is uncoloured. HANGING DROPS. The green bodies can be easily separated from the tissue containing them by teasing it out in water, filtering through fine bolting silk, and fractionating the filtrate by means of a centrifuge. A great deal of oil is present in this filtrate, but it remains in suspension on centrifuging, and after a few washings a residue is obtained consisting of little but the green bodies and bacteria.
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