MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 32 ( ,> 



the button) in shallow water. Occasionally they inhabit short, vertical burrows, which they con 

 struct for themselves in the sandy uiud, but most of the species pass their life hidden, in the shelter 

 which they find upon the reef. 



The most conspicuous characteristic of the genus is the great enlargement of the claws of the 

 first pair of walking legs. Both claws are large, but one of them is enormous, and it serves as a 

 most formidable, weapon of offense and defense. In some species this large claw nearly equals 

 the body in size, and it is usually carried stretched out in front of the body, but one species carries 

 it folded down under the body and hidden, ready to be instantly pushed out to make a rapid thrust 

 at any enemy. 



In nearly all the species the, large claw terminates in hard, powerful forceps. The claw or 

 dactyle is provided with a plug, which fits into a well or socket in the other joint and probably 

 serves to prevent dislocation. When the forceps are opened the dactyle is raised so that the plug 

 just rests in the mouth of the socket. As soon as the claw is released it is suddenly and violently 

 closed, as if by a spring, and the solid stony points striking together produce a sharp metallic 

 report, something like the click of a water hammer, and so much like the noise of breaking glass 

 that I have often, when awakened at night by the click of a little Alpheus less than an inch long, 

 hastened down to the laboratory in fear that a large aquarium had been broken. In the open 

 water the report is not so loud as it is when the animals are confined in small aquaria, but Al- 

 pheus is so abundant in all the Bahama Sounds that a constant fusilade is kept up at low water all ' 

 along the shore. The animals are remarkably pugnacious and they will even attack bathers. They 

 are known to the inhabitants of the out islands as "scorpions," and are much dreaded, although 

 their attacks are harmless to man. The snapping propensity is exhibited both in the water and 

 out by both sexes, and if two males or two females, either of the same or different species, are 

 placed together in an aquarium, a most violent combat at once takes place, and quickly ends by . 

 the destruction of one or both. Some species appear to pinch with the large claw, but it is more 

 frequently used like a saber for cutting a slashing blow. The edge of the movable joint is sharp 

 and rounded, and the animal advances warily to the attack with the claw widely opened and 

 stretched out to its full length. Watching its opportunity it springs suddenly upon its enemy, 

 instantly closing its claw with a violent snap and a loud report, and cutting a vertical sweep witli 

 its sharp edge. I have often seen Alpheus heterochelis cut another completely in two by a single 

 blow, and the victim is then quickly dismembered and literally torn to fragments. 



The abundance of these animals in coral seas is well shown by the fact that of the twenty 

 species which are known to inhabit the shores of the North American continent we found twelve, 

 or more than half, upon a little reef at Dix Point, a few rods to the eastward of our laboratory at 

 New Providence, in the Bahama Islands. 



Of the thirteen species which we found in the islands several are new, and as none of them 

 have ever been adequately described, an illustrated, systematic description of all the species is 

 now in preparation by Mr. Herrick. The present memoir deals only with the embryology and 

 metamorphosis of the genus. This is a new field, for nothing whatever has as yet been published 

 upon the embryology of any species of the genus, and all our knowledge of the metamorphosis is 

 contained in two short abstracts without illustrations on the metamorphosis of a single species, 

 Alpheiifi lieterochelis. Eggs have now been obtained from all thirteen of the Bahama species, and 

 the first larval stages of most of them have been reared from the eggs in aquaria in the laboratory, 

 and the metamorphosis has been traced from actual moults. 



THE METAMORPHOSIS OF ALPHEUS. 



One of the most remarkable results of our study of the various species of the genus Alpbeus 

 is the discovery that, while there is such a general similarity as we might expect between the 

 larval stages of the different species, the individuals of a single species sometimes differ more from 

 each other, as regards their metamorphosis,' than the individuals of two very distinct species. 

 This phenomenon has been observed by us and carefully studied in two species Alpheus hetcro- 

 chelis and Alpheu-g mtulcyi and it is described in detail, with ample illustrations, in the chapter on 

 the metamorphosis of Alpheus. In the case of the first species the difference seems to be geo- 

 graphical, for while all the individuals which live in the same locality pass through the same series 



