jj.^^ John H. Gerould, 



Transformation into the Larva occurs at the end of the 

 second day, when the yolk membrane, which has been stretched by 

 the growth of the trunk, is torn open and cast off. The cilia, 

 slipping through the pore canals, are generally uninjured by this 

 process. 



The larval cuticula, already of considerable thickness, is formed 

 beneath the yolk membrane before the latter is shed. 



The muscular system now includes, besides the chief and accessory 

 dorsal and ventral retractors (in all, eight pairs), three pairs of small 

 neuromuscular rudiments within the trunk, two of which are ventral, 

 one dorso-lateral. The entire apical and prototrochal region is drawn 

 backward by repeated spasmodic contractions of the retractors. 

 Complete introversion of this part of the body takes place as soon 

 as the coelom is established by the splitting of the mesoderm. The 

 circular muscles, particularly the middle sphincter, now become 

 functional. 



The prototroch cells degenerate from within outward. Loose 

 masses of yolk granules break off from their inner side, and during 

 the repeated introversions, are left within the coelom of the trunk. 

 Finally the entire cytoplasm of these cells, transformed 

 into yolk granules, and their nuclei also, are passed 

 i n 1 t h e c e 1 m i c f 1 u i d. The overgrowth of the region vacated 

 by the large prototroch cells takes place chiefly from the dorsal 

 side, backward from the apical plate, and ventrad and forward from 

 the posterior part of the dorsal cord. The process consists partly 

 in cell-division, partly in the flattening and spreading of the cells. 

 LarvalDevelopment. The somewhat cylindrical, worm-like 

 larvae creep on the bottom {Ph. goiildii), or twirl near it {Ph. vulgare). 

 They are opaque from the presence in the coelomic fluid of an 

 abundance of yolk granules, which have been derived from the 

 prototroch cells. Two sorts of coelomic corpuscles also occur in small 

 numbers, the larger of which are probably the free nuclei of the 

 degenerated prototroch cells. They are of the same size as the 

 amoebocytes of the adult. The fate of these larval corpuscles was 

 not traced. 



The ventral nerve cord, oesophageal connectives, and supra- 

 oesophageal ganglion now contain fibrillae. The eye spots, the 

 rudiments of the sensory and glandular organs in the skin of the 

 adult, and the larval musculature are described. 



The nephridia appear in Ph. gouldii at about the sixty-fifth 



