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ZOOLOGICAL SOCIETY BULLETIN 



the lens, with two black bands running back 

 from head to tail on either side of the alimen- 

 tary tract. In a day or two these bands change 

 from black to scarlet. Three to seven days 

 elapse after the embryos have separated from 

 the yolk and before they develop the scarlet 

 stripes. Then the yolk gradually disappears 

 and they begin to get acquainted with their 

 many wonderful appendages and to make as 

 vigorous use of them as narrow quarters per- 

 mit. Within from two to five days after ac- 

 quiring the red stripes they leave the pouch 

 and the stripes soon fade to yellow. The body 

 remains white until the animal is about 8 mm. 

 long, when it assumes the adult coloration. 



The eggs of European species are said to 

 pass into the pouch from the sixth thoracic seg- 

 ment and to undergo external fertilization. In 

 the American species the only exit to the pouch 

 is at the front end, under the mother's head, 

 which arouses the suspicion that the female 

 fresh-water shrimp, like the female lobster, may 

 hold the sperm until the eggs are laid, making 

 the extrusion of the eggs and their fertilization 

 coincident. 



As might be expected, some mothers are more 

 intelligent than others, and therefore better moth- 

 ers; and these, by throwing back the In ad. 

 enlarge the exit for the benefit of the struggling 

 young, of which three may be endeavoring to 

 escape at the same instant, though only one can 

 possibly pass at a time through the door that 

 leads to the watery exterior. Nearly one hun- 

 dred per cent, emerge right side up. With their 

 long antennae they explore the exit, and appear 

 as though chucking their mother under the chin 

 in familiar farewell. Finally a tiny body pro- 

 trudes half way. the owner assures itself that 

 all is well, and confidently waving its antennae 

 as if to send an introductory greeting to the 

 new world, gives a quick spring out of the 

 brood pouch. And now. provided with all the 

 instincts of its forbears and the ability to for- 

 age for itself, it is prepared to take its infin- 

 itesimal part in the drama of aquatic life. It 

 holds no further communication with its moth- 

 er, and in all likelihood would not recognize 

 her should it ever meet her again. 



In the development and growth of these ani- 

 mals, the strangest irregularity prevails, and 

 this begins in the egg. They are therefore not 

 all born the same hour, and rarely the same day. 

 Sometimes seven will follow one another out 

 of the brood pouch within as many minutes, but 

 it may be five days before the entire brood 

 has emerged. The number in each brood in the 

 cases observed, varied from eight to thirty-four 

 (with two extreme cases of one and forty-three). 



amounting in a number of instances to twenty- 

 three, of which thirteen were born one day and 

 ten the next. 



When the tiny creature is born, its eyes are 

 noticeably connected by pigment strips with the 

 brain ganglion, and instead of being divided 

 into many, irregular black or reddish brown pig- 

 ment spots like its parents', consist each of 

 three large, oval, seal-brown patches. Eyes of 

 this type have been given various names, — 

 ocelli, ommatidia, eye-spots, facets, etc. 



Like insects, crustaceans have faceted eyes, 

 and in some species they form, under magnifi- 

 cation, a beautiful mosaic. Herrick estimated 

 that the lobster's eye contains about 14,000 

 facets. An interesting feature of the faceted 

 eye is that an object, instead of being seen as 

 a single image, as with eyes of higher structural 

 development, is reflected in every facet; so that 

 if it were possible to bring an object within 

 the range of vision of all the facets simultane- 

 ously, the lobster would see 28.000 small images 

 of it. The facets in the eye of an adult fresh- 

 water shrimp number thirty or less, and, lack- 

 ing definite form, are not beautiful, resembling 

 nothing so much as a sliced pomegranate; but 

 in another, closely allied but evidently less 

 primitive species (Carinogammarus macro tint us) 

 often found with the fresh-water shrimp, the 

 eye is from birth geometrically laid out in hand- 

 some black-and-white mosaic. The animal fur- 

 ther differs from the shrimp in being nearly 

 black and having both pairs of antennae of 

 equal length, with an invisible spine ornament- 

 ing each joint along the back. Some specimens, 

 when dissolution is approaching, turn red. in- 

 stead of white like the shrimp. 



The development of the body, eyes and an- 

 tennae, do not keep strict pace with one an- 

 other. The shrimp's growth, like that of other 

 young creatures, is largely determined by the 

 healthfulness of its environment, — uncontami- 

 nated water, abundant food and green plants all 

 being conducive to strong and healthy bodies ; 

 yet under identical conditions a dozen shrimps 

 born the same day and kept in the same recep- 

 tacle, will show remarkable variation in devel- 

 opment. 



The eye in some specimens begins to break 

 ii]) on the ninth day. five brown spots first ap- 

 pearing in place of four, afterwards becoming 

 six ; then more appear until there is a coales- 

 cence of the eye pigment. In some specimens 

 this occurs at three or four weeks, in others 

 later. The seal brown eye may change to the 

 adult magenta or black at sixty days. 



The antennae at birth number each seven 

 joints or segments, and growth is effected, not 



