EMBRYOLOGY OF CLEPSINE. 279 



cula, the seventh and largest one of which lies behind and 

 stretches through five somatomeric chambers. 



The diverticula of the anterior and posterior regions are entire, 

 while those of the central region are lobed. The lobes repeat 

 themselves with considerable regularity on each pair of diverti- 

 cula. The seventh pair show five subdivisions, corresponding 

 to the number of body-chambers, and each subdivision presents 

 the principal marginal notches seen on the anterior diverticula 

 of this region. The first pair is an imperfect counterpart of the 

 seventh ; it reaches forward through two chambers instead of 

 five, and has a corresponding number of subdivisions. The 

 seventh pair of diverticula and that part of the alimentary canal 

 included between them (intestine and posterior region of stomach) 

 recall the picture of the iliac bones and coccygeal style of the 

 frog. 



The intestine is a narrow tube, which ends in the dorsally^ 

 placed anus. Diaphragmatic septa are interposed between the 

 walls of the diverticula, and through the central and ventral 

 emargination of these septa passes the trunk of the stomach. 

 How do these diverticula arise? Figs. 49 to 55 are supposed 

 to answer this question in part. 



The somatomeric division begins soon after the conjunction 

 of tlie germ-bonds, and progresses from the neural, outward and 

 upward, towards the haemal side, and at the same time cen- 

 tripetally. The centripetal growths of the mesoderm are the 

 septa above described. In stage 50 (three days after exclusion) 

 the septa (marked by transverse lines) have already reached the 

 median lateral line of the embryo, but their centripetal growth 

 has not yet made any marked changes in the form of the yolk. 

 On the sixth day after exclusion all intermediate forms are found 

 between figs. 50 and 52. The neural side of the embryo is still 

 much longer than the haemal, and the latter is, therefore, con» 

 cave, and the face of the terminal disc turned upward. Ths 

 septa have already cut sufficiently deep into the yolk to mark 

 oft" the caecal divisions and the primary regions of the future 

 stomach. The seventh diverticulum (c. 7), which was at first 

 simple, now has three of its five subdivisions. As this diverti- 

 culum lengthens backward, the yolk in the intestinal region 

 diminishes (fig. 53). In fig. 54 the intestinal part has become 

 still more reduced, and the seventh pair of caeca correspondingly 

 larger. At this time the dorsal side is nearly as long as the 

 ventral, and the face of the sucker is at right angles to the Ion ■ 

 gitudinal axis of the embryo. In stage 55 (six days after 

 exclusion) all the principal form -differentiations of thealimentar} 

 tract are to be seen. 



At about this time the eyes become visible as two pairs 



VOL. :^Vin. NEW SKll. T 



