456 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



ix. (1) Tbe majority of the Alphei luitcli as zoea-ltke larvse, while two species are 

 known, A. heterochelis and A. saulcyi, in which the metamorphosis is abbreviated. This shortening 

 of tiie metamorphosis appears to be directly related to the habits ami environment of the species. 

 A. heteroclielis has one metamorphosis at- Beaufort, North Carolina, a more abbreviated develop- 

 ment at Key West, Florida,, and, it we are right in considering the Bahamau form as a member of 

 this species, at Nassau, New Providence, the metamorphosis is complete or unabbreviated. The 

 Nassau form of Alpheua snnlri/i either has the metamorphosis greatly abridged or it hatches with 

 all the external characters and the instincts of the, adult. When we inquire into the modes 

 of life of these species we. tiud the remarkable fact that the Nassau Alphcus s<tu lci/i is a parasite or 

 commensal, living in the pores of certain sponges, and the metamorphosis is completely absent or 

 profoundly modified. The Floridian Aljilien/i l/i'/croc/iclin is a parasite in sponges, and has its 

 metamorphosis greatly abridged. Tin- Keaufort lirli'r<H.-liclix, which must be regarded as descended 

 from the Kloridiau stock, iias its metamorphosis less abridged than in the latter case aud it is 

 uouparasitic. However, we still tiud it occasionally producing small eggs, indicating a tendency 

 to revert to the old metamorphosis, long since abandoned. Even if \ve decide that the Nassau 

 heteroclielis has had a different genealogy from that of the, Beaufort variety, we still have strong 

 evidence to show that the metamorphosis of the species may change in accordance with a change 

 in habits and environment. 



\'iu'/iitinn and Haliitx. (L') Aljilti/nn ln'tcrocln-iix of Beaufort presents an interesting variation 

 in the structure of the small chela, which appears to be a sexual one. 



(.".) In many Macronra as well as I'.rachyonra, and especially in the Alpliens, one of the claws 

 is enormously enlarged, often nearly e<pial in size to the rest of the body of the animal. This great 

 chela may be either on the right or left side of the body, but it almost invariably follows that all 

 the young of a brood have, the large claw on the, same side, indicating that this characteristic is 

 inherited from the parents, and that where both of the. latter have the right or left claw enlarged 

 they give rise to right and left handed broods, respectively. 



(4) Alpheux xiutlri/i presents very profound variations, and some of these varieties would 

 undoubtedly be regarded as distinct species by systematic zoologists if the intermediate forms 

 were, unknown. These forms are described and discussed in Sections v aud vn of Part First. 



.Species living side by side show no tendency to commingle, and hence we conclude that the 

 striking varieties which we arc here met with are not the result of hybridism, but are confined 

 to a single species. Two well marked varieties occur, which I have distinguished as Alpheus 

 xitiflcyi, var. brevicarpus, and A. sanlcyi., var. loni/icaipim. Between these forms every intermediate 

 stage is found. 



The color variations in this species are also exceptionally marked. In all respects the males 

 appear to be more variable than the females. The structural peculiarities of the mother appear 

 to a large extent in the offspring, and if the swamping effects of intercrossing should be elimi- 

 nated it is likely that this species would soon become separated into at least two distinct forms. 



It seems most probable that the change in habits or environment which this species has under 

 goue, has acted as a direct stimulus to variation. 





of the Larva of Alphcux xnulcyi. (j) The structure of the first larva of this Alphens 

 reaches a very high degree of complexity, which is but little exceeded by that of the mature adult 

 form. 



The green gland does not yet appear to have an external opening. The five pairs of gills 

 present at this time are also rudimentary, and the reproductive organs are only represented by a 

 small cluster of large cells on either side of the middle line, between the digestive tract and the 

 anterior end of the heart. For the histological details, reference must be made to Section i or 

 Part Second. 



The Oi-in-i/ <m<l Orai-i/ut KIJIJ. (fi) The ovary consists of an external stroma of muscular aud 

 connective tissue and a lining epithelium. The ova arise from the lining epithelium, and each egg 



