Rebbuabt 26, 1909] 



SCIENCE 



347 



the egg, and with hooks embedded in its 

 tough chitinous " glue " they hold on literally 

 "for dear life," often grasping the same 

 stalk with both chelse. So strong was this 

 seizing and holding instinct that the young 

 when forcibly separated from- the mother 

 would sometimes lay hold of a suspended 

 string, and were thus successfully reared until 

 the period of dependence was over. Once 

 fixation with the claws is successful, the tel- 

 son-thread breaks and the young remain thus 

 attached by the claws alone for a period of 

 from four to thirteen days, according to con- 

 dition, when they molt to the second stage. 



At the second molt this crayfish is for the 

 first time free, and soon begins to descend the 

 parental pleopod, climbs over its mother's ' 

 body, and makes short excursions in the 

 neighborhood, returning again and again to 

 the ahna mater and the family brood. 

 Hitherto it has been sustained solely by the 

 generous supply of yolk inherited from its 

 egg-state, but since the egg-stalks and cases, 

 as well as the cast skins which remain at- 

 tached to the mother, disappear at this time, 

 it is thought that they are eaten by the young 

 and constitute the first direct food that they 

 receive before beginning to forage for them- 

 selves. 



The second stage Astacus develops a strong 

 climbing instinct; it is brilliantly arrayed in 

 red and blue pigments as well as the colors 

 which the transparent skin transmits from 

 liver and yolk. The swimmerets are func- 

 tional, and the appendages generally are 

 garnished with numerous sensory setae; but 

 the powerful "propeller" or tail-fan is not 

 completed by the liberation of the sixth and 

 largest pair of pleopods until the third stage 

 is reached. Then the little crayfish becomes 

 very active, voracious and pugnacious, fre- 

 quently losing its limbs at the " breaking 

 joints" and as freely regenerating them. At 

 the fourth stage the rudimentary first pair of 

 pleopods make their appearance, and probably 

 in the males only. 



The Oambarus affinis, which Professor An- 

 drews has studied with marked success, lays 

 its eggs in March or April, and carries them 



about seven weeks. Its eggs are smaller and 

 rather more numerous than in the Astacus, 

 and the yoimg are correspondingly less ad- 

 vanced at the time of hatching. They do not 

 leave their mother until the third stage, 

 but are associated with her for about two 

 weeks only, or for nearly the same length of 

 time as in Astacus. In this case also at 

 hatching the young are tethered, and pre- 

 vented from escaping from the mother, but by 

 ail " anal thread " of a peculiar character. 

 When this young escapes from the egg it 

 leaves behind it a larval cuticle or molt, which 

 sticks at two points only, on the side of the 

 mother to the egg-membranes which are ad- 

 herent to her, and on that of the child to a 

 portion of the intestine where its cuticular 

 lining is not at first set free. As a result of 

 the tension this embryonic molt is stretched 

 and crumpled with a tendency to turn the 

 abdominal part inside out. This telescoping 

 and partial inversion of the discarded cuticle 

 is checked by the flat molted plate of the tel- 

 son with the resultant production of a narrow 

 creased ribbon, the " anal thread," which is 

 firmly fastened to the intestinal wall. 



The young of this crayfish attain a length 

 of two inches during the first summer, when 

 they may be fertilized by a male of corres- 

 ponding age and lay fertile eggs in the follow- 

 ing spring. In one case a female which was 

 reared from the egg laid eggs herself in two 

 successive seasons, when about one and two 

 years old, and when somewhat more than two 

 and three inches long respectively. Andrews 

 remarks that since the young of this 0am- 

 iarus reared in captivity not only laid fertile 

 eggs, but since this was repeated in the next or 

 third generation there would seem to be no 

 obstacle to the domestication of this crusta- 

 cean and rearing of it upon an extensive 

 scale. 



The first two stages of the young are thus 

 not only peculiarly modified for association 

 with the parent, but in some way unknovrn, 

 correlated structures of a most delicate kind, 

 not to speak of instincts, have arisen in both 

 to bring this about. These may be compared 

 to the first three stages of the lobster, in 



