MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 377 



twenty-fourth inch, but two females were found which carried a few bunches of very small eggs, nor- 

 mally <ilu('d to tJio anterior swiinnieretvS. These eggs measured only one tifty-third to one sixty-Hfth 

 inch in diameter, that is, the contents of the smaller was about one-twelfth that of the larger egg. 

 This occasional production of very small eggs exhibits a tendency, which is still present in 

 the species of this locality to-day, to revert to its old metamori)hosis long since laid aside. 



III.— THE ABBREVIATED DEVELOPMENT OF ALPHEUS AND ITS RELATION TO T/lE ENVIRONMENT. 



Related species, as a rule, resemble each other more in their early stages of derelopment than 

 in their adult state. This is not, however, invariably true, since all animals, whether young or 

 adult, must adapt themselves to their environment or be destroyed. It is probable that animals 

 in all stages of growth are equally plastic and tend to vary with the varying conditions of life. 



The early life in large classes of the animal kingdom, as fishes, birds, and manjinals, is si)ent 

 either in the protecting membranes of the egg or within the body of the i)arent, and is thus but 

 slightly affected by external conditions, and suffers little change in consequence. In other groups, 

 on the contrary, and in the Crustacea in particular, the case is very different. Uere the young 

 are usually hatched in a very immature condition, and lead a life of their own at the surface of 

 the ocean, wholly independent of their parents. They have accordingly adapted them.selves to this 

 mode of life, and the variations thus entailed have led to the production of the zoi^a, a locomotor 

 larva, fundamentally different from the adult. We may regard the zol-a as a secondary, adaptive 

 form, directly descended from an ancestral protozoi-aii type. After passing a longer or shorter 

 period (usually of several weeks) at the surface of the sea, the adult state is gradually reached 

 through a comi>licated series of changes, and the animal adapts itself to new conditions on the sea 

 bottom or on the shore. 



Now, if the habits of the adult and larva should tend to converge, if the adults should adapt 

 them-selves to an entirely new environment, which it is necessary for the young to become fitted 

 for at once as soon as hatched, we would expect that the zoi-al stages, formally assume<l to bridge 

 over a gap which no longer exists, would be dropped or shifted to the egg. This seems to have 

 actually taken place, and is illustrated in a remarkable manner in the genus Alpheus. 



Most of the species, which are very numerous, inhabit the shores, in common with many 

 related forms, and, as already stated, they abound on coral reefs. They all, as a rule, lialcli as 

 zoiia-like and have a complicated metunioridiosis. Two species have been discovered, however, 

 which have adopted a parasitic life, and in ea(;li the larval period is accelerated. In one, which is 

 .semiparasitic, the metamorphosis is partially abbreviated; in the other, which is completely para- 

 sitic, the metamorphosis is completely lost. Still more interesting and significant is the fact that 

 one of the species in one locality is nonparanitic and has a complicated metamorphosis, while the same 

 species from another locality is itarasitic and has the metamorphosis abridged. 



We will now cou.sider more particularly the history of these two forms, in order to make a 

 clearer comparison. The species are — 



t Alpheus heterochelis, from Nassau, New Providence. 



(1) ? Alpheus heterochelis, from Keaufort, North Caraliua. 

 ( Alpheus heterochelis, from Key West, Florida. 



(2) Alpheus saulcyi, from Nassau, New Providence. 



ALPHEUS HKTEROCHELI3 FROM THE BAHAMAS. 



This species, found at Nassau, exemplifies the development commcm to the genus, as .seen, for 

 instance, in A. normani (Kingsley), which is closely associated with it, A. minus Say, and in many 

 other Bahaman forms. It is one of the common species at Dix Point, and may be found in abun- 

 dance on the shore of the little bay, in pools left by the ebb tide, under shells or loose fragments 

 of coral. 



First larva (length = i inch). — The three pairs of maxillijteds, each with long exopodites ending 

 in feathered hairs, are the principal loi^omotor organs. Two pairs of riidiinentarv thoracic legs 

 are present. All the abdominal segments, but none of their appendages, are formed. 



