4:1)6 MEMOIRS OF TEIE NATIONAL ACADEMT OF SCIENCES. 



Metamorphosis.— [1) The inajority of the Alpbei hat(;h as zoea-like larvre, while two species are 

 known, A. hetfirnchelis and A. sanlcyi, in which the metanioiphosis is abbreviated. This shortening 

 of the inetainorpiiosis appears to be directly related to the habits and environment of the Sjiecies. 

 .4. lu'terocheiis Jias one metamorphosis al- Beaufort, Nortli Carolina, a more abbreviated develop- 

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

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

 Nassau form ot Alpheits saulci/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 find the remarkable fact that the Nassau Alpheus saulcyi is a ))arasite or 

 commensal, living in the pores of certain sjionges, and the metamor[)hosis is completely absent or 

 profoundly modified. The Floridian Alpheus heterovhdi-s is a parasite in si)onges, and iias its 

 metamorphosis greatly abridged. Tlie Beaufort heterochelis, which must be regarded as descended 

 from the Floridian stock, has its metamori)hosis less abridged than in the latter case and it is 

 nonparasitic. However, we still find it occasionally producing small eggs, indicating a tendency 

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

 hetcrochelis has bad a rlifferent 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. 



Varintion and Habits. — (i!) Alpheus heterochelis of Beaufort presents an interesting variation 

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



(3) In many Macroura as well as Bracbyoura, and especially in the Alpheus, one of the claws 

 IS enormously enlarged, often nearly equal 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) Alpheiis saulcyi presents very j>rofound variations, and some of these varieties would 

 undoubtedly be regarded as distinct si)ecies by systematic zoologists if the intermediate forms 

 were unknown. These forms are described and discussed in Sectious v and Yii of Part First. 



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

 striking varieties which we are here met with are not the re.sult of hybridism, but are confiued 

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

 saulcyi, var. brevicarpus, and A. saulcyi, var. longicarpus. 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 oUspring, aud if the swamping eflects 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 

 gone, lias acted as a direct stimulus to variation. 



Structure of the Larva of Alpheus saulcyi. — (o) The structure of the first larva of this Alpheus 

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

 foriii. 



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

 present at this time are also iiidinientary, and the rei)roductive 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 Ovary and Ovuriun Eyy. — (<i) The ovary consists of an external stroma of muscular and 

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



