152 O. C. GLASER. 



and granular, are very irregular in shape, the cytoplasm being 

 almost invisible, in irregular strands, or crowded closely against 

 the cell boundaries. In the center some of the cells have a large 

 clear space in which the nucleus lies. The nucleoli sometimes 

 occur in the clear vacuoles which are scattered about in the 

 nuclei. Many of the latter are in process of amitotic division. 



Around the outer margin of the lateral and ventral walls of the 

 oesophagus many of its bounding cells seem to have broken 

 down, whereas others are clearly engaged in this process. By 

 this means the outline is made extremely irregular, being frayed, 

 and fringed with granules and the fragments of cells. This 

 breaking down of the cells, their general vacuolated appearance, 

 the occurrence of amitosis, and the finely divided state of the 

 chromatin in the nuclei, all indicate that these cells are actively 

 engaged in metabolism, and the simplest supposition is that they 

 are engaged, as Osborn has suggested, in the process of digestion. 



That something is leaving these cells is demonstrated by their 

 appearance. I believe therefore that in the course of their activity 

 as digestive cells, they excrete waste products, and that these 

 pass across the "body cavity " into the cavity of the velum, 

 transude through its basal membrane into the external kidneys 

 and through these ultimately to the exterior. The arrows are 

 intended to give a graphic representation of this process. 



Homologies. - The earlier writers who considered the functions 

 of the external kindeys of gastropods fall into two general groups, 

 those who affirm and those who deny that these organs are renal 

 organs. The same writers however have been at much greater 

 discord with regard to the homologies. Thus Salensky ('72) 

 homologized the external kidneys of Calpytrea sincnsis with the 

 primitive kidneys of pulmonates. Fol ('75) did the exact reverse 

 by attempting to homologize the " Urnieren " of pulmonates with 

 the primitive kidneys of prosobranchs. Bobretsky ('77) who de- 

 scribes the "Urnieren" of Nassa nnitabilis, Natica, and Fusns, 

 seems to have accepted the homologies advocated by Salensky. 

 Biitschli ('77) in the same year, however, in a paper on Pahidina 

 invipara took strong exception to Fol's homology. He pointed 

 out that this supposed homology was between totally different 

 structures, and that while the primitive kidneys of Palndina 



