300 ANIMAL PARASITES. 



a single central spot or nucleus, but the larger ones contain 

 several internal cells or nuclei of various sizes, and are probably 

 the mother-cells of the smaller cells, which are undoubtedly the 

 germs of the seminal cells. Meissncr also states that limpid 

 cells, with a vesicular nucleus and nucleolar body, are produced 

 as male germ-cells in the blind extremity of the testicular tube. 



As the smaller cells mentioned by Thompson advance into the 

 next darker portion of the testicular canal, each individual cell 

 surrounds itself with the soft granular mass contained in the 

 canal, and increases about three times in size. In this way are 

 produced oval structures, slightly pointed at the two ends, which 

 are at first without an enveloping membrane, but are subse- 

 quently provided with one. They become clear on pressure, or 

 by the application of acetic acid, and then exhibit the nucleus or 

 nucleolar body distinctly. Thompson regards the granular mass 

 in the testicular tube as an analogue of the vitelline mass, and 

 thinks that the granular mass, which is probably a product of 

 secretion of the tube, is deposited from without upon the cells, 

 and not produced in their interior. Meissner describes these 

 cells as filling themselves with a granular mass, analogous to the 

 vitelline granules, and therefore from the interior. At the same 

 time the nucleus disappears, and the cells become polygonal by 

 pressure. 



The seminal cells thus formed now advance into the lower 

 constricted portion of the section of the testis, which is filled 

 with a granular mass, when they are, according to Thompson, 

 100 — Too ' i u diameter, round, and surrounded by a distinct ex- 

 ternal membrane. According to Meissner the granules now draw 

 back on all sides from the cell-wall, and cease to be homogeneous. 

 According to Thompson the} r experience two different changes, 

 divide into several segments, usually four (Bischoff and Thomp- 

 son), but according to Meissner, erroneously, into eight, and then, 

 in each of these segments, short, linear, radiating structures are 

 formed, the granules, according to Meissner, arranging themselves 

 regularly, in a radiate form, around a clear, enucleate centre. 

 The centre also divides into small nuclei, which unite with the 

 above-mentioned segments, and thus are produced cells with 

 daughter-nuclei, which however do not advance far in segmenta- 

 tion. The daughter-nuclei form the foundation for the produc- 

 tion of the development-cells of the seminal corpuscles ; these 

 nuclei, advancing at regular distances apart to the periphery of 



