174 



H. V. WILSON AND BLACKWELL MARKHAM 



ing eggs of Chorophilus feriarum which had been artificially in- 

 seminated February 15th. It was early singled out by Mr. T. 

 E. Rondthaler as one in which the blastopore did not close, and 

 was kept under more or less continuous observation. It elon- 

 gated and became somewhat flattened dorsoventrally, the yolk 

 plug occupjdng a median dorsal position in the posterior part of 

 the body. Immediately behind the yolk plug two tail buds, 

 one left, one right, appeared. They both early acquired a spiral 



Fig. 3 Chorophilus larva. Dorsal view, bit, base of left tail; brt, base of 

 right tail; trt, tip of right tail; ya, exposed yolk area. X 25. 



Fig. 4 Ventrolateral view, from the left, of larva shown in figure 3. le, left 

 eye; In, left nostril; m, mouth; tU, tip of left tail; trt, tip of right tail; ya, exposed 

 yolk area. X 25. 



curvature in different planes. External gills, which are small in 

 this species, developed. With their disappearance and the steady 

 increase in size of the head and trunk region, the yolk plug grad- 

 ually shifted over toward the left side of the bodj^ One tail, 

 the left, was thus carried into a position which was distinctly 

 ventral (fig. 4). The other tail, the right, which gradually be- 

 came much the stouter, took up a position which was distinctly 

 dorsal, its basal part directly in line with the median longitudinal 

 axis of the trunk (fig. 3), 



