PubuisAed wit/i t/ie approbation of t/ie Board of Trustees VOL. XI.—No. 97.1 BALTIMORE, APRIL, 1892. [PRIcE, 10 CENTS. MORPHOLOGICAL NOTES. FROM THE BIOLOGICAL LABORATORY OF THE JOHNS HOPKINS UNIVERSITY. EDITED BY WILLIAM K. BROOKS, PH. D., PROFESSOR OF ANIMAL MORPHOLOGY AND DIRECTOR OF THE CHESAPEAKE ZO6LOGICAL LABORATORY. THE EMBRYOLOGY AND METAMORPHOSIS OF THE Jn these features all the other Arthropods are like the Crustacea, but MACROURA. another consideration, tile fact that, with few exceptions, the higher Crus- tacea are marine, renders the problem of their life-history much more intel- By W. K. BRooKS and F. H. HERRICK. ligible than that of any other class of animals. So far as the ontogenetic Ilistory of the metamorphosis of a larva is a [Theintroductorychapter of an illustratedmemoir byW. K. Brooks and F. H. Herrick, which will appear in the Fourth Memoir of Volume V of tlse Memoirs of the National recapitulation of ancestral stages in the evolution of the species, its reten- Academy of Sciences.] tion at the present day must depend to a great degree upon the persistency of those external conditions to which the larval stages were originally No great group of animals is more favorable than the Crustacea for the adapted. study of the history and significance and origin of larval forms, for these This is true at least of all free larvae, which have their own battles to animals possess a number of peculiarities which seem to rendcr the problem fight assd their own living to get, and while a larva inside an egg or within of their life-history both unusually interesting and significant, and at the a brood pouch may possibly recapitulate obsolete ancestral stages, the sur- same time unusually intelligible; nor are these peculiar features exhibited, vival of a free larva depends upon its adaptation to its present environment. to the same degree, by any other great group ef animals. As compared with the ocean the inorganic environment of terrestrial or The body of an Arthropod is completely covered, down to tlse tip of each fresh-water animals is extremely variable, and changes in climate, elevation microscopic hair, by a continuous shell of excreted matter, and as this chit- and continental configuration are accompanied by corresponding changes inons shell is not cellular it cannot grow by the interpolation of new cells, in enemies, competitors and food, so that the conditions which surround a nor can it, like the excreted shell of a molluse, grow by the deposition of modern terrestrial larva must in nearly every case be very different from new matter around its edges, for there are no such groxving edges, except those under which the remote ancestors of the species passed their life; but in a few exceptional cases, such as the barnacles. Once formed and hard- while this is also true to some degree of marine animals, thleir inorganic envi- ened, the cuticle of an Arthropod admits no increase in size, and as soon as ronment is comparatively stable, and the persistence of so many ancient it is outgrown it must be discarded and replaced by a new and larger one. marine types shows that the changes in the organic surroundings of The new shell is gradually excreted, in a soft condition, under the old one, marine animals take place much more slowly than corresponding changes and as soon as this is thrown off tile new one quickly becomes fully distended on land. and solid. As the result of the very nature of the chitinous shell, and This fact, joined to the definite character of the changes which make up the method of renewal which its structure entails, the growth of an Artbro- the life history of a marine crustacean, renders these animals of exceptional pod, from infancy to the adult condition, takes place by a series of well- value fqr the study of the laws of larval development, and for the analysis marked steps or stages, each one characterized by the formation of a new of the effect of secondary adaptations, as distinguished from the influence cuticle and by a sudden increase in size. of ancestry; for while Claus has clearly proved that adaptive larval forms In most Arthropods the newly-born young are very different in structure are much more common among the Decapods than had been supposed, his from the adults, and growth is accompanied by metamorphosis. As the writings and those of Fritz Muller show that no other group of the animal changes of structure are necessarily confined to the moulting periods, the kingdom presents an equal diversity of orders,families, genera and species, stages of growth coincidewith the stages of change in organization, and there in which the relation between ontogeny and phylogeny is so well displayed, is none of the indefiniteness which often characterizes the different larval but while proving this so clearly, Claus’ well known monograph also shows stages of animals with a more continuous metamorphosis. On the con- with equal clearness, that this ancestral history is by no means unmodi- trary, the nature of each change is as sharply defined and as characteristic fied, and that the true significance of the larval history of the higher as the structure of the adult itself. As tile moulting period is frequently a crustacca can be understood only after careful and minute and exhaustive time of inactivity, the animal may then undergo profound changes without comparison and analysis. inconvenience, and the successive steps in the metamorphosis of an Arthro- Greatly impressed by this fact, I begun nearly ten years ago to improve pod are not only well marked, but often very profound as well. the opportunities that were afforded by the marine laboratory of the 66 JOHNS IJOPIUNS [No. 97. Johns Hopkins University, for obtaining more complete and detailed The adults are found in pairs, a male and a female swimming together knowledge of the larval stages of a number of Macroura, and this ~vorkhas side by side, an(l exhibiting evidence of strong conjugal attachment to been prosecuted at every opportunity, np to the present time. Some of my each other. results have been published in my monograph on Lucifer, in the Phil. The most noteworthy fact in its history is its world-wide distribution, Trans. Royal Soc. for 1882, and others are incorporated in my report on the and the question whether this can be a result of any peculiarity in its Stomatopoda collected by H. M. S. Challenger. structure or habits at once suggests itself. This memoir contains the life histories of a number ofadditional species, We should expect, on general principlcs, to find the least specialized based in part upon my own studies at Beaufort, =4orthCarolina, and at Green species the most widely diffused; and one which holds its ground in so Turtle Cay and New Providence in the Bahama Islands, but chiefly upon many parts of the world, and without any change of structure finds a safe the researches which one of my students, Mr. F. H. Herrick, has carried on and congenial borne in seas so widely separated might be expected to be of under my general supervision. In 1886, he undertook, at my suggestion, indefinite or slightly specialized habits but this is not the case. In structure, the study of the embryology and metamorphosis of the Macroura, and in habits, in color and in external appearance, and also in its metamorphosis, devoted three years to this subject under my direction, and the results Stenopus is one of the most highly specialized of the crustacea; and it which follow are almost entirely due to his zeal and energy. He has com- owes its ability to survive in nmany seas to the accuracy and delicacy of its pleted the study of several subjects upon which I had previously made a adjustment to a narrow range of conditions, rather than to indefinite and beginning, so that my own unfinished notes have been incorporated with vague adaptation to many conditions. his researches, and our respective shares in the work are as follows. The Its antennae are unusually long and slender, and the acuteness of its chapter on Gonodactylus is entirely based upon my own researches: the senses, together with its very remarkable alertness; the cinickness with chapter entitled “Alpheus, a study in the development of the Crustacca,” is which it perceives danger and the rapidity with which it escapes, have entirely the work of Mr. Herrick; the one on the metamorphosis of Alpheus undoubtedly aided it in holding its own wherever it has gained a foothold is based upon our combined studies, and that upon Stenopus is almost in a suitable locality; and no crustacean, with the exception, possibly, of entirely the work of Mr. Herrick, as my own contributions to this life his- Gonodactylus chiragra, is better adapted for life in a coral reef. tory are of minor value except so far as they supplement his work. It is well protected from enemies by a thorny armor of hooked spines, I shall now aive a brief outline or summary of the chief results which which cover all the upper surface of its body and limbs, and as all the are described in detail in each chapter. hooks point forwards the attempt of an enemy to swallow a Stenopus must be difficult and painful. THE LIFE-HISTORY OF STENOPIJS HISPIDITS. These facts no doubt account for its survival, and the length ofits pelagic During the six seasons which I spent at Beaufort, North Carolina, I larval life is beyond question an aid to its wide dispersal, and to the dis- captured in the tow-net, at different times, some six or seven specimens of covery of new homes.