354 s. HATTA : 



form the anterior continuation of the cardiac tube or the truncus 

 arteriosus. An irregular cell-structure {x) is seen on either side 

 above the dorsal corner of the body-cavity and inside the tract 

 of the anterior cardinal vein. It is this structure about which I 

 could not at first decide with certainty whether it was a slice of 

 the hind wall of the branchial chamber or a part of the pro- 

 nephric tubule. All the cases examined, however, point towards its 

 being a part of the tubule ; the structure is detected in the anterior- 

 most part of the ])ody-cavity which wedges in, at about this 

 stage, to the branchial region with a sharp angle (see fig. 97). 

 The narrow space (fig. 08, pp.c.) found intervening between the 

 structure and the peritoneal walls is a part of this cavity. One 

 might suppose that the space may be the coelomic cavity of the 

 branchial region ; but, the sjmce between the parietal and the 

 visceral peritoneum of the branchial region is consolidated already 

 in the preceding stage, being filled up with variously shaped cells 

 of mesenchymatous nature (see fig. 07). 



In the next following section shown in fig. 00, a tubular 

 structui'e {'pt.2) with an oval outline is seen on either side at 

 the place where the pronephric tubule ought to be found. Its long 

 axis is directed just like a tubule (compare with figs. 101, 102, ifcc. ). 

 This is doubtless a part of a pronephric tubule ; but the corres- 

 ponding nephrostome which ought to be found either in the 

 section in front (fig. 98) or behind (fig. 100), can not be detected 

 in either of them. The nephrostome must, therefore, be looked 

 upon as having degenerated ; and since this pair of the tubules 

 is, in fact, detected underneath the fifth myotome, it must be 

 identified as the second pair of the tubules. The section represented 

 in fig. 100 shows on both sides the cross-sections of the collecting 

 duct {ccL). On the left side, a cellular structure connects the 



