424 J- T. Cunningham 



interfere with the processes of prepariug or cutting-. In this case it was 

 not necessary to trace the injection through a number of successive sec- 

 tions. because the sections being- thin, the passage not very minute and 

 the direction of the sections the same as that of the passage , two or 

 three of the series showed the whole canal from the cavity of the peri- 

 cardium to that of the kidney. One of these sections is given in tig. 3, 

 where the dorsal part of the kidney is to the left and the ventral to the 

 right. The pericardial cavity, pc , is seen at the top of the section and 

 from it runs down a narro w canal containing the blue injection and 

 opening below into the cavity of the kidney, hc. In the middle of its 

 length the canal is divided into two by a band of connective tissue, x^ 

 which appears to be chiefly cellular. On the right of the figure is showu 

 the wall of the branchial cavity consisting of muscular fibres and connec- 

 tive tissue intertwined in all directions , et , and containing irregulär 

 blood- Spaces, U. The epithelium coveriug the wall of the branchial 

 cavity is composed of very small cells , like the external epithelium of 

 the rest of the surface of the body, and is represented as seen under 

 low power by a dark line. No epithelium can be seen lining the wall of 

 the pericardium, but the canal of communication is lined by an epithe- 

 lium composed of cells of considerable size ; whether this epithelium is 

 ciliated or not I bave not determined ; cilia cannot be detected in the 

 sections. 



The cavity of the kidney is divided by fiat trabeculae of connective 

 tissue which start from the wall of the cavity, into a number of commu- 

 nicating Chambers and passages of various sizes ; and the cavity commu- 

 nicates with the exterior by the small circular opening whose external 

 Position and appearance has already been described, fìg. 2 eo. In order 

 to examine more minutely the nature of this opening I cut a series of 

 sections through the part of the kidney containing it. For this purpose 

 the posterior end of the kidney was taken and cut into sections, whose 

 piane is perpendicular to the wall of the branchial cavity and to the 

 dorsal surface of the kidney. One of these sections passing through the 

 external opening is represented in fig. 4 ; where the wall of the branchial 

 cavity and the opening of the kidney are seen ou the right side. The 

 opening is seen to be lined by a columnar epithelium continuous with 

 that of the branchial cavity, on one side and passing into the renai 

 epithelium on the other. The contractions and expansions of the opening 

 are due to the ordinary musculature of the body wall. 



The appearance presented by the renai tissue under a low power 

 is seen in figs. 3 and 4. The trabeculae in section are seen as thin 



