196 W. E. ALLEN. 



lacking some indefinable quality of the old tissue (cf. Figs. 1-5). 



Much the same things may be said about tin- intestinal 

 epithelium. In thi- ti--ue cilia are well developed on the third 

 (lav and it is e\idently functional l>y that time but it retain*; 

 some slight embryonic features to about the eighth or ninth day. 



Septa are lir-t distinguishable in the embryonic mass as radial 

 columns of cells (Fig. i) extending partly across the cu-lomic 

 space. They rapidly fuse into a continuous membrane reaching 

 evident maturity by the fifth day (cf. Figs. 1-6). 



The longitudinal muscle layer of the body is first noticeable 

 as a very thin, somewhat scattering layer of long, spindle-shaped 

 cells just inside the epidermis (Fig. i). It does not change very 

 definitely except for increase of thickness and compactness. Al- 

 i hough otherwise well developed by the seventh day at latest, 

 it is not of typical thickness until later (cf. Figs. 1-5). 



The nerve cord is recognizable on the fourth day and almost 

 mature on the fifth. It is apparently typical by the seventh day. 

 Note in Fig. 5 the ventral localization of nerve cells in the cord so 

 characteristic in this group of worms (cf. Figs. 3-5). 



The embryonic peritoneum seems recognizable by location on 

 the third day but is well developed by the fifth (Fig. 5), and in 

 evident maturity by the seventh (Fig. 4). 



The blood vessels were not easily followed. The ventral vessel 

 is unquestionably well formed by the fourth day. Both were 

 observed in some specimens of the sixth and both are certainly 

 mature by the ninth (cf. Figs. 3-5). 



The study of chlorogogue was very unsatisfactory. It would 

 seem that it should show well soon after maturity of the intestinal 

 wall at least and it is distinguishable on the sixth day and there- 

 after, but no specimen was found showing it in typical condition 

 even at the tenth day. It is possible that the sand in the intestine 

 affected its preservation more than that of the other tissues. 



The seta 1 are easily followed even in toto mounts. 1 he 

 embryonic seta sacs are well formed on the tilth day, and the 

 setai with all their muscles seem to be I'unctional by the seventh. 

 There is no question of their maturity bv the loih da\ < 1 ig. 4). 



Nephridia were rather diltieiill lo identify. An irregular mass 

 of embryonic nephridial cell*- was first located, mainly by position, 



