ON THE ORIGIN AND DEVELOPMENT OF THE CEMENT GLANDS IN ETROPLUS MACULATUS (BLOCH). BY S. JONES. (From the University Zoological Research Laboratory, Madras.) Received October 1, 1937. (Communicated by Prof. R. Gopala Aiyar.) Introduction. WHrLE engaged in working out the development of some brackish water fishes of Adyar,* I had the opportunity to investigate the development of the cement glands in two Cichlid fishes, Etr@lus maculatus and E. sura- tensis. These glands have the same function as in the larvm of Ganoids, Teleosts, Dipnoids and Anura in which similar organs have been discovered. The developmental origin of these larval organs has been worked out in the case of Ganoids, Dipnoids and Anura. In the first group they arise from the endoderm whereas in the latter two, they are of ectodermal origin (Kerr, ]919). Though cement glands are known to occur in some tropical Teleosts like Etr@lus, Pterophyllum, Sarcodaces and Hyper@isus, no work on their origin has been done so far to my knowledge.~ The present paper deals with the cement glands in one of the local forms, Etr@lus maculatus. These structures, found only in the aquatic larvm of some fishes and amphibians, are all purely larval organs primarily concerned with the attachment of the larvm to some foreign object to prevent their being swept away by currents. Except in the case of the larvze of Ac@enser, where they are transformed into barbels, the cement glands degenerate and disappear in course of time. In the case of Etr@h~s also the glands are most active during the earliest larval stage and then atrophy as soon as the young fish is capable of swimming about. Historical. Ganoids.--It was Agassiz (1879) who first worked on the cement glands of fishes when he dealt with the function, degeneration and disappearance of the gland (suctorial disc) in Lepidosteus. He did not mention anything * S. Jones, "Observations on the Breeding Habits and Development of Certain Brackish Water Fishes of Adyar, Madras," Proc. Ind. Acad. Sci., (B), 1937, 5, No. 6. t S. Jones, Curt. Sci., 1937, 5, No. 9. 251 B4 252 S. Jones as to its origin. In 1881, Balfour dealing with the same form, considered the suctorial papill~e of the gland as epiblastic sensory thickenings and later in 1882, Balfour and Parker speak of them as modified cells of the mucous layer of the epidermis pouring out a sticky secretion. Phelps (1899) as a result of bet work on Amia calva said that the gland is endodermal in its origin. Subsequently, Reighard and Phelps (1908) gave a detailed account of the origin and development of the gland in Amia calva and they attributed a similar (endodermal) origin to the gland in Lepidosteus. About the same time appeared the work of Eycleshymer and Wilson (1.908) and these authors agreed with regard to the endodermal nature of the glands in Amia calva. Kerr (1906 and 1907) worked out the development of the gland in Polypterus senegalus (Budgett's collection) and found it to take its origin from the endoderm. He was not at the time aware of the work on Am(a calva by Phelps. Kupffer (1893) thought that the cement organs of Acipenser sturio was of ectodermal origin. Sawadsky (19ll) basing his work oi1 Acipenser ruthenus said that the organ in question actually originates from the ectoderm. Thus the endodermal development of the cement glands in Ganoids was finally settled. Dipnoids and Anura.--Among the Dipnoi cement glands are known to be present only in Lepidosiren paradoxa and Prot@terus annectans, where they have been found to be of ectodermal origin (Kerr, 1903 and 1919). Assheton (1896) and Bhaduri (1935) worked out their development in Rana temporaria and R. afghana respectively and found them to originate from tile outer layer of ectoderm. The difference in these two groups is that in the Dipnoi tile secretory cells of the glands develop from the inner layer of ectoderm whereas in the Anura they develop from the superficial layer of ectoderm. Tdeosts.--Cement organs are known to occur only in a very few tropical Teleosts. It was first discovered by Budgett (1901) in the larvae of two African fishes, Sarcodaces odoe (Characinidae) and another which he provi- sionally determined as IIyper@isus bebe (Mormyridae). Assheton (1907) when dealing with the sense organs and mucous canals in the larvae of Gymnarchus niloticus and Heterotis niloticus mentions about the presence of mucus secreting glands on the head. It is possible that they are similar to the glands in Ityper@isus and Sarcodaces though Budgett who examined the living specimens did not observe any adhesive organs. ProbaBly they are degenerate. They are known in some Cichlids like Etroplus suratensis. (Willey, 1911), E. maculatus (Sundara Raj, 1916)and Pterophyllum eimekei Otigi~ ~ Development of CemenL Glands i1~ E. maculatus ( Bloch) 253 (Lieberkind, 1931). Of these Cichlids the last one is South American and the other two are South Indian forms. From the literature available it appears no work has been done so far on the origin of the gland in Teleosts. Lieberkind (1931) described the well- developed and active gland of the five days old larva of P. eimekei and mentions its absence in a 10 days old one. But due to lack of sufficient material he could not work out the origin of the gland. Cement Organs of Elroplus maculatus.--In the case of this fish, as soon as it hatches out, the glands can be seen as three pairs of symmetrically arranged conical projections each with a depression at the top. One pair is situated at the anterior extremity of the head near the olfactory organs, whereas the other two pairs are found close together dorsal to the eyes (Figs. I and 2). These are larger than the anteIior-most pair. The glands FIo. 1.--Newly hatched Iarva. X 22. 1, 2 and 3 = Cement organs. Fit;. 2.--Larva 2nd Day. X 22. FIC. 3,--A group of young Iarv~e resting at the bottom attached by their mucous threads, x 6. secrete mucus till the fourth day after which they become inactive and gradually atrophy. During this short period the secretion helps to keep ~he larvae in one place under the care of the parents, thus affording protec- tion (Fig. 3). Origin and DeveIopment.--The cells of the gland rudiment gradually become distinct in the thirty-eight hours old embryo. The rudiment develops as a thickening of the inner layer of ectoderm (Fig. 4). The cells are tong and conical with the nuclei at their base. They soon curve over enclosing a space, the gland cavity, roofed over by the thin superficial B4~ 254 S. Jones layer of ectoderm. Fig. 5 is a transverse section of the head passing through the middle pair of glands in a fifty-four hours old embryo. FIG. 4.--Section through a gland rudiment of a 38 hours old embryo, glr., gland rudiment. I-iatching takes place seventy-two hours after fertilization at which time all the three pairs of glands are active. The secretion of the" gland cells fills the cavity and bursts open the superficial layer of ectoderm which gets peeled off. Now the cavity widens. This is accompanied by the raising of the sides of the cavity which results in the formation of a deep gland cavity opening to the outside. The superficial laver of ectoderm extends tip to the edge of the gland ctlp (Fig. 6). No " brush border" of the kind mentioned by Bhaduri (1935), lining the gland cells in Rana afghana, has been observed. Several larvae are found anchored to one place by mucous threa~ emanating from the cement glands. The parents have, as has been already observed, the curious habit of transferring their broods from place to place and each time, the young ones attach themselves once more by mucouS Origin F:P Development of Cement Glands in E. maculatus ( Bloch) 255 threads. In the attached condition the larvae remain with the dorsal surface of the head touching the substratum with the body held at an angle to the ground and the tail vibrating incessantly. When disturbed they break off from their moorings and move off in this characteristic position trailing a quantity of dirty mucus behind them. They again collect together in groups and a fresh attachment is effected. Fie. 5.--Section through the head of a 54 hours old embryo passing through the middle pair of cement glands. FIe. 6.--Section through the cement organ 1st Day. • 380. Fla. 7. ,....... 2nd Day. • 380. Abbreviations : hr., Brain; co., Cement Organ ; E., eye ; glc., Gland cavity. The glands grow in size (Figs. 7 and 8). Meanwhile the interspace between the pairs of glands increases. Gradually, they get flattened out and the cells become vacuolated. The cell walls become indistinct and degene- ration sets in. The rapidity of the process can be understood by the change 256 S. Jones the glands have undergone by the fifth and the sixth day (Figs. 0 and 10). As soon as they shrink in size the superficial layer of ectoderm from the FIG. 8.--Section through the cement organ 4th Day. • 380. FIe.. 9......... 5th Day. x 380. FIC.. 10. , ....... 6th Day. X 380. sides, which at this time gets considerably thickened, grows over the rapidly degenerating structures which are soon lost. By the seventh day it is hardly possible to locat~ their position. The structure and position of the cement glands of E. suratensis are exactly as in E. maculatus. Though their origin and development have not been worked out it is not likely that there will be any difference.