294 THE ZOOLOGIST. 



by its bright eyes and the saddle-shaped mass of black pigment 

 in the abdomen.* 



Immediately it had jerked itself free from the egg-mass, each 

 larva began to swim vigorously in a vertical, or nearly vertical, 

 position at, or close to, the surface of the water by rapid 

 vibrations of its tail. None of the larvae pursued a straight 

 course through the water, their movements being exceedingly 

 irregular. One of them, for example, went round and round in 

 circles of about half an inch in diameter, at the same time re- 

 volving rapidly on its long axis. Several of them were to be seen 

 moving round in such a way that their tails described small, 

 while their heads described larger, circles. None of them moved 

 tail foremost. After a few minutes of swimming a larva would 

 cease to move its tail, and sink to the bottom to rest for two or 

 three minutes, and then it would give a convulsive jerk and 

 begin to swim again. These observations were made on the 

 larvae which were in an aquarium, containing nearly thirty 

 gallons of well-aerated and constantly-moving sea-water, standing 

 in a fairly dark spot. The behaviour of a dozen of the larvae 

 placed in a white enamelled bowl containing about a gallon of 

 still sea- water in the direct light from a window was of a similar 

 character. The larvae in the larger tank seemed always to be 

 fairly evenly distributed throughout the tank, and there was no 

 tendency in the larvae to congregate behind the glass front.! 



At the beginning of the second day after hatching, the larvae 

 seemed able to keep a more even course through the water, and 

 to swim with greater vigour. If the motions of its tail ceased, 

 however, a larva would immediately turn head downwards and 

 fall slowly to the bottom, where it would usually lie for a few 

 minutes, its little eyes shining so brightly that it was not at all 

 difficult to detect them amongst the shingle of the bottom. 

 After several ineffectual attempts I was able to time one which 

 swam obliquely upwards through an almost straight course of 

 about fourteen inches immediately behind the glass front of the 

 tank ; it took fifty-four seconds to swim this distance, so that 



* Cunningham (op. cit. p. 73) points out that the pigment is not in the 

 skin but in the peritoneum over the region of the stomach and rectum. 



f Fabre-Domergue & Bietrix (op. cit. pp. 174-9) describe the attraction 

 of light on the larvse of Coitus bubalis. 



