40 WRIGHT AND MACALLUM. [Vol. I. 



masses with the largest number of cells having the smallest 

 nulcei, and as the number of cells present in the different 

 masses varies in arithmetical proportion, we have come to the 

 conclusion that a single parietal cell, when it falls into the cavity 

 of the lobule, gives rise by repeated division to a sphere or 

 spermatogemma, each division being represented by a clump 

 or mass of cells, which vary in number with the number of 

 divisions the cells have undergone. The irregular masses of 

 cells resulting from the final division become spherical, the 

 individual cells arranging themselves radially round a sort of 

 segmentation-cavity, and then moving toward the periphery of 

 the sphere. 



Our observations as to Spermatogenesis in Sphyranura agree 

 with the main details of the brief sketch given by Schwarze' of 

 this process in Distomum endolobiim, but are at variance with 

 this observer's in one important respect, namely, as to the 

 share which the cytoplasma takes in the formation of the 

 spermatozoid. This author describes the head of the sperma- 

 tozoid as arising out of the nucleus while the cytoplasma gives 

 origin to its tail. The structures in question in Sphyranura and 

 their mode of development may be so easily observed that we 

 cannot permit ourselves to doubt the conclusion indicated 

 above, — that the spermatozoids arise wholly from the nuclei 

 of the sphere or spermatogemma. 



Kerbert's and Looss' descriptions of spermatogenesis in Dis- 

 tomes appear to us inexact in some points. They find cres- 

 centic cells, the concave face of each of which may contain 

 the heads of a number of spermatozoids. Sommer found the 

 heads inserted in the substance of the crescentic cells. We 

 have observed appearances like those figured by Looss and 

 Kerbert, but they are accidental rather than natural. For 

 instance, the nuclei of the parietal layer of the lobule, and the 

 nuclei like them in its cavity, are very frequently in that initial 

 stage of division in which a part of the- nuclear membrane is 

 free from contact with the chromatin-filament, this part answer- 

 ing to the "Pole" of Rabl. Oblique views of this Pole often 

 give the appearance of a crescentic cell, and if the heads of a 

 sheaf of spermatozoids are seen over against one of these we 

 get the appearances figured by the above-named observers. 



' Zeit. Wiss. Zool., XLIII., 73. 



