THE YOUNG OF THE CRAYFISHES ASTACVS AND CAMBARUS 61 



scarcely more than one-half the length of the other larvae. The young that are 

 shaken off dart, swimming, about in the water but soon settle to the bottom and 

 climb up upon one another in heaps or try to climb up at the corners of the 

 dish and upon water plants. 



The tendency to climb onto the mother is very strong so that when a 

 female walks along swinging her pleopods laden with young she often gathers 

 up free young that are walking about, as these when touched by a pleopod 

 may not spring away but turn and climb onto the mass. In fact early in the 

 third stage a larva that fell to the bottom, apparently for the first time, stood 

 with head end elevated and quickly responded to the presence of a passing 

 pleopod. Even if lying upon their backs they quickly seize and mount the pleo- 

 pod of a passing female. A piece of white cheese-cloth, however, did not appear 

 to stimulate them to climb upon it and when a lump of rough cement, a model 

 of a toad, was left in the aquarium very few got on it, most of them preferring 

 the mother. 



Possibly the young receive chemical stimulus from the mother that aids 

 them in returning to her. That they responded to some chemical stimuli is 

 most probable and the following facts may be interpreted on this basis. When 

 the mother feeds, the young gather under her mouth and even after the food 

 is gone they remain as if excited by chemical substances coming from the 

 mouth parts of the female. It was also found that while the young climb onto 

 a dead female and even over the exposed surface of the freshly broken abdo- 

 men, after some days they remain on the rest of the surface but not upon the 

 broken surface where chemical substances due to decay probably existed. 



During the time the larva? in the third stage associate with the parent the 

 large collections of old egg shells and skins on the pleopods disappear and 

 are probably eaten up by the larvae since their intestines contain minute setae 

 that might come from their old cuticle and since in Astacus, Chantran ('71) 

 foimd that the larvae eat their shells and cast off cuticles. It is therefore possible 

 that one reason the young remain with the mother is that this food supply on 

 the abdomen acts as a stimulus to them. 



However, along with whatever chemotactic movements there may be, there 

 are other factors concerned in the association of the young with the female as 

 indicated by the few following experiments, which tend to show that the 

 young are controlled in part by responses to light and to gravitation and con- 

 tact. Thus when a small paste-board table was put under the water the young 

 collected on the under side of the horizontal paste-board and remained stand- 

 ing upon it, in an inverted position. When the paste-board was then turned up- 

 side down the young scattered in a few minutes so that half were off the paste- 

 board and some were under it in its new position. In crawling under such a table 

 the young reared up and seemed to be trying to reach it above their heads as if 



