MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 377 



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

 mally Allied to the anterior swimmerets. These eggs measured only one fifty-third to one sixty -fifth 

 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 iu 

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



III. THE ABBREVIATED DEVELOPMENT OF ALPHEUS AND ITS RELATION TO THE ENVIRONMENT. 



Belated species, as a rule, resemble each other more iu their early stages of development 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 tishes, birds, and mammals, is spent 

 either in the protecting membranes of the egg or within the body of the parent, and is thus lint 

 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. Mere 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 themselves to this 

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

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

 form, directly descended from an ancestral protozoeau 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 complicated series of changes, and the animal adapts itself to new conditions on the sea 

 bottom or ou the shore. 



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

 themselves 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 zoeal stages, formally assumed 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, hatch as 

 zoea-like and have a complicated metamorphosis. Two species have been discovered, however, 

 which have adopted a parasitic life, and iu each 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 nonpuranitic and lias a complicated metamorphosis, while the same 

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



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

 clearer comparison. The species are 



f Alpheus lieterochelis, from Nassau, New Providence. 



(1) 1 Atyhcus lieteroeltcUfi, from Beaufort, North Caralina. 

 ( AlpheiiK hctcrochclin, from Key West, Florida. 



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



ALPHEUS I1ETEROCHELIS FROM THE BAHAMAS. 



t 



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

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

 other Bahainan forms It is one of the common species at Dix Point, and may be found iu 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 = J- inch). The three pairs of maxillipeds, eacli with long exopodites ending 

 in feathered hairs, are the principal locomotor organs. Two pairs of rudimentary thoracic legs 

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



