MEMOIRS OF THB NATIONAL ACADEMY OF SUIEXCES. 320 



tlic baUom ill sljiillow water. Occasionally they inhabit short, vertical burrows, which they con 

 struct for themselves in the sandy mud, but most of the species pass their life bidden in the shelter 

 \vhi(;li they liiul upon the reef. 



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

 first pair of walking legs. P.oth claws are large, but one of them is euormous, and it serves as a 

 most formidable weapon of often.sc 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 i)uslied out to make a rai)id thrust 

 at any enemy. 



In nearly all the sjjecies the large claw terminates in hard, jiowerful forceps. The claw or 

 dactyle is provided with a plug, which Jits 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 month of the scujket. As soon as the claw is released it is snddeidy 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 Aljilieus less than an inch long, 

 hastene<l 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 atta(!ks are harmless to man. The snapping propensity is exhibited l)oth 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 (ilaw, 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 

 stre^hed 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 with 

 its sharp edge. I have often seen Alphetis heterochelis cut another com[)letely 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 th& 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 wo 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 ]»ublis"!ied 

 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, 

 Alpheus lieterochelis. Rggs 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 acpiaria in the laboratory, 

 and the metamorphosis has been traced from actual moults. 



THE HmTAMORPHOSIS OF ALPHEUS. 



One of the moat remarkable results of our sttuly of the varijus species of the genus Alpheus 

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

 larval stages of the <Iifferent species, the individimls 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 lietero- 

 chelis and Alpheus suulcyi—nud 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 individu.als which live in the same locality pass through the same series 



