MORPHOLOGY OF CYCLOSTOMATA. 341 



little. The internal lumen of the tubules are ]iut not only in 

 wide communication with the peritoneal cavity, but also in direct 

 continuation with one another through the collecting duct, which 

 consists of a regular columnar epithelium-cells arranged radially 

 and now encloses a conspicuous lumen. 



In the foremost of these twelve sections (fig. 64), we notice that 

 a structure {pt.l) consisting of a few cells projects at the outer 

 corner of the proximal edge of the lateral plates and lies in contact 

 with the outer wall of the myotome on either side. This structure is 

 found under the anterior border of the fifth myotome and T infer 

 that it is a remnant of the first pair of the pronephric tubules which 

 begins to decline in the present stage. The reason wh}- it is found 

 not under the fourth myotome as in all the stages hitherto des- 

 cribed but beneath the anterior border of the fifth myotome, 

 consists probably in its shifting backwards ; for we find, in this 

 series of sections, another pair of the tubules under this same fifth 

 myotome. A comparison of this figure with fig. Q>ö representing 

 the next posterior section will make the matter clear. On the 

 left side of fig. 65, the same remnant structure {pLl) together with 

 the collecting duct [ed.), which connects the first and the second 

 tubules can be observed, while the cross-section of the collecting- 

 duct in the corresponding intersomitic plane is seen on the op- 

 posite side {ed.). The next following section is shown in fig. Gß ; 

 the tubules (pt.2) on both sides communicate freely with the 

 peritoneal cavity ; these are found beneath the hind part of the 

 fifth myotome and are the second pair of the tubules ; the open- 

 ings (list. 2) to the peritoneal cavity ^are, therefore, the second 

 nephrostome of the pronephros. The tubule on the left side is 

 weaker than that on the right, since a larger part of the left tubule 

 is visible on the section next posterior which is represented in fig. 



