ZOOLOGICAL SOCIETY BULLETIN 



i:i 



ing but small, living, moving animals. In har- 

 bor water, whose density is rarely over 16/1000. 

 the shrimps remain active for two days and 

 some survive twice as long. In pure ocean wa- 

 ter with a density of 28/1000, they do not last 

 an hour, but remain active about twenty-five 

 minutes, which is ample time for the sea horse 

 to secure them. 



When all its appendages are counted, the 

 shrimp proves to be possessor of over thirty. 

 All are useful, the long antennae being sense 

 organs, quite as good as eyes, and the short 

 antennae understudies that take the part of the 

 long ones if they become injured or broken off. 

 The masticating organs (maxillipeds ) are just 

 behind the head, and the appendages following 

 these (gnathopods) are used principally to cap- 

 ture and carry food and other objects, and to 

 clean the antennae. The five pairs of legs 

 (paraeopods) with which the animal walks, kicks 

 and clings, are quite indispensable — the poste- 

 rior pairs so astonishingly long and strong that 

 the shrimp can support both the weight of its 

 own body and a heavy piece of food, while 

 clinging to the glass side of an aquarium or a 

 plant leaf by the three long legs of one side 

 of the body only. The three pairs of feathery 

 "pleopods,'' corresponding to the swimmerets 

 of lobsters and crayfishes, are constantly at 

 work driving currents of water against the gills 

 to aerate them (the gills being reticulated sacs 

 not noticeable until about the twenty-sixth day. 

 suspended just in front of the pleopods). The 

 tail appendages (uropods) also have their re- 

 stricted uses, aiding especially in jumping and 

 walking. 



Seven pairs of the appendages serve as de- 

 fensive organs. — the ten legs and four gnatho- 

 pods. It may be mentioned that mules, pos- 

 sessing only four legs and under the necessity 

 of standing on at least one, are no kickers at 

 all in comparison with shrimps that can stand 

 on their heads and throw out fourteen service- 

 able appendages with a claw on the end of each. 



The shell is so delicate and thin that, under 

 the microscope, the colorless corpuscles of the 

 blood can plainly be seen traveling through the 

 plates, legs, antennae, etc., passing each other 

 in jerking though rhythmic processions up and 

 down the living way. 



While the shrimp does not live in burrows, 

 it is devoted to empty snails' shells, in which 

 it takes true delight in hiding, protruding the 

 long antennae to detect the presence and char- 

 acter of passersby. These antennae are so ex- 

 quisitely sensitive that the shrimp cannot bear 

 to have them meddled with, and if visitors prove 



too curious, it soon quits the shell and swims 

 away. 



The shrimps do not breed until about 8 mm. 

 long, and this would seem to be when they are 

 three or four months old. The development and 

 growth of the young are not regular as in many 

 animals. We can tell approximately when a 

 kitten will open its eyes and when it will lap ; 

 but we cannot say with equal assurance that a 

 fresh-water shrimp thirty-five days old will 

 have eyes like its parents, be i mm. long, and 

 exhibit a certain number of joints in its an- 

 tennae. 



In captivity the shrimps breed the year round, 

 and it is possible they do so in a state of na- 

 ture. They are said not to hibernate in winter, 

 but merely to seek deeper water. When placed 

 in a dish containing water but three inches deep 

 and subjected to freezing temperature (32°), 

 the shrimps, when ice formed at the top, merely 

 sank to the bottom, and suspended animation 

 ensued. On the raising of the temperature to 

 47°, they all became active again. Although 

 they are comparatively hardy, a difference of 

 2° at the extremes of temperature affects them 

 powerfully and suddenly. At 91° they are ac- 

 tive, at 06° drop dead; at 3 1° they swim near 

 the surface, at 32° they sink, motionless. 



The glistening body of the fresh-water shrimp 

 is divided into fourteen joints or segments, the 

 head occupying one. the thorax seven, the ab- 

 domen six. 



The brood chamber, snugly enclosed within 

 the coxal plates directly behind the head and 

 lying close against the body, extends from the 

 second to the sixth thoracic segment. The coxal 

 plates are SO transparent as to permit a full 

 view of the black eggs whicii can almost be 

 counted with the naked eye if one has accus- 

 tomed his eye to observe such small objects, 

 and their general development is not difficult to 

 follow under magnification. The brood chamber 

 which, when empty, lies well within the coxal 

 plates, enlarges with the segmentation of the 

 eggs until it extends below the plates. It is 

 of elastic consistency and incubation in all speci- 

 mens observed lasted two weeks, though it may 

 actually last longer. 



The eggs contain a food yolk, and as this 

 separates from the embryos they lie across the 

 yolk as many embryonic fishes do. They arc 

 black. — first round, then slightly ovoid, — and 

 the mother changes their position by pressing 

 against the brood pouch with her head and 

 pushing its contents back and forth. The young 

 move slightly in the black stage. Later they 

 appear white to the eve. though colorless under 



