252 s. GOTO; 



III. Enlerocœl and Hydrocœl. 



From their genetic connection us well as from tlieir undergoing 

 simultaneous changes, it ^vill be most convenient to treat these two 

 systems together. 



The general aspect of the changes which these two systems under- 

 go is shown in Plates XIX-XXI, and we shall use them as basis in 

 the following description. I start with stage B, i. e., a fully developed 

 bipinnaria, since the earlier stages have, in my opinion, been satis- 

 factorily studied by previous observers. The hydro-enterocœl at the 

 stage just mentioned is represented in Figs. 2-4, in its left, 

 ventral, and right aspects. As will be seen from these tigures there 

 is but one cavity, but we may distinguish difterent portions of it. 

 Since we know that the cavities on the two sides of the body were, 

 after their separation from the primitive gut, entirely separate and united 

 secondarily in the prasoral lobe we shall distinguish them as the right 

 and left enterocœls. In either of them we may again distinguish two 

 portions, the antei'ior and posterior. In the left enterocœl these two 

 portions are pretty sharply marked off by the presence of the pore- 

 canal and a sudden constriction which the cavity undergoes at this 

 point, due apparently to the development of the hydrocœh In 

 the right enterocœl, how^ever, these two portions grade insensibly into 

 each other, althouo-h in an earlier staçre a sHo-ht constriction can often 

 be observed at the corresponding leveh At this stage, therefore, we 

 may already distinguish four portions, viz., the right and left anterior 

 nnd the right and left posterior, and we shall subsequently see that 

 their separation becomes more and more accentuated as metamor- 

 phosis progresses. 



We must now take a more careful view of the several portions of 

 the body cavity. Tlie tw^o anterior enterocœls freely communicate 



