31 



stroke of the antennae, they expand widely, and drive the' 

 animal upwards, while, on the upward stroke, they bend 

 downwards at their tips and the body is only carried slightly 

 lower. The final result is that the larva is carried upwards 

 by a series of dancing movements (about 4 per second), which 

 are continued with short periods of rest till the animal reaches 

 the surface of the water. 



The factor which determines the direction of movement 

 is apparently the light, and once at the surface they rapidly 

 congregate towards the most illuminated corner of the tank. 



The rapidity with which they seek the light, and their power 

 of discriminating between shght differences in illumination, 

 were well illustrated by placing several in a glass dish in a 

 room with two windows having slightly different outlooks. 

 They quickly approached the more illuminated side, and, on 

 this source of light being lessened, they as quickly moved 

 towards the other source of illumination. In this lateral 

 movement the main axis of the body is, of course, more or 

 less changed in position. 



Should movement cease for a short time in the ascent, the 

 body sinks rapidly, as it is still laden with a certain amount 

 of heavy yolk, lodged in the region of the large diverticula of 

 the future hver, the anterior end of the ahmentary tract and 

 the thinner intestine. This yolk is apparently sufficient to 

 tide over the interval between the first and second moult. 

 Under the microscope the mouth appendages are seen to be 

 in active movement, but their spines and denticulations 

 are as yet covered by cuticle, and apparently the animal takes 

 no food at this stage. 



The duration of this stage is very short. A number of 

 individuals on one occasion was observed given off from the 

 parent in the morning and, by midday, they had all changed 

 into the second stage. 



The significance of this larval stage, of so short duration, 

 and in which the animal may take no food, is doubtless con- 

 nected with that fact that the larva changes into a second 

 stage which procures its food at the surface of the water, 

 and which is so organised that an upward movement is not 

 easy. Though the duration of the first stage is only for a 

 few hours, it is sufficiently long to enable the larva to ascend 

 the few fathoms of water in which the parent Hves. 



In the second stage the legs become expanded and hang 

 down on each side of the body, all except the last pair (the 

 third walking leg) which are long and are trailed out behind. 

 The body now assumes a horizontal position and progression 

 is mostly parallel to and near the surface of the water The 



[C.P. 5-'i3-] 



