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RANDOLPH. [Vol. VII. 



mention of the peritoneum. He refers to large cells that appear 

 occasionally in a series of cross-sections with the comment that 

 they are probably the "chorda cells " of Semper. 



The neoblasts must in my view be regarded as specialized 

 embryonic cells set apart for the formation of new mesodermic 

 tissue immediately after the fission of the worm. Since they 

 are closely connected in origin with the peritoneal tissue, they 

 are probably to be regarded as belonging to it. 



Kiikenthal (12) figures cells in Tubifex very like the neoblasts, 

 lying among the muscles as seen in tangential section. This 

 corresponds to the position of the neoblasts, since, from the 

 curvature of the body-wall and also from the varying degree 

 of contraction of the muscles, in sections in certain planes the 

 cells are apparently embedded in tissue. Kiikenthal gives these 

 as one source of the lymphoid cells of Tubifex. Since, however, 

 he expressly states that he has never seen these granulated cells 

 either enter or leave the muscles, and that the lymphoid cells 

 have a different structure, it occurs to me as possible that what 

 he has seen are really the neoblasts. 



In different forms of Annelids described by Eisig (6), Kiiken- 

 thal, and others, the peritoneum gives rise to ova and to lymphoid 

 cells. In the Phylactolasmata the eggs arise from the coelomic 

 epithelium of the budding region (4). In Pyrosoma also, accord- 

 ing to the researches of Seeliger (20), the mesoderm of the 

 budding region gives rise to eggs. 



It has been suggested to me by Professor E. B. Wilson that 

 the neoblasts are comparable to ova. That unlike ova they 

 give rise only to mesoderm seems to me not out of harmony 

 with this conception, since the elements of the two other germ 

 layers may be suppressed from lack of need or of opportunity 

 to develop. They may represent the ova of the primitive worm 

 which were originally produced in every somite, but which have 

 ceased to develop in any except a few of the segments of the 

 anterior region of the body. In this connection the recent paper 

 of Meyer (14) on the derivation of the Annelids is of great 

 interest. If almost the whole Annelidan mesoderm is repro- 

 ductive tissue, the explanation of the regenerative power of 

 peritoneal tissue is simplified to the last degree. In any case 

 there is a close connection in the development in general 

 between ova and peritoneal cells. 



