BLACKMAN: THE SPERMATOGENESIS OF SCOLOPENDRA. 21 



not at all well developed, and often when seen in very thin sections 

 plainly shows its reticular character. It is much less clearly marked 

 than the nuclear membrane, for while the latter stands out very plainly 

 in the vesicle stage, the former is often very difficult to distinguish 

 as a definite structure. 



The spermatocytes when they have reached the vesicle stage are of 

 two well-defined types. The history of one of these types, the smaller, 

 was described in considerable detail in my first paper (Blackmail, :01) 

 on the spermatogenesis of Scolopendra. The larger type was merely 

 mentioned there, but a second paper (Blackmail, :03) deals with these 

 larger ones almost exclusively. As the succeeding changes in the cells 

 of the two types present considerable differences, I think it advisable to 

 characterize them briefly at this time. The differences between the two 

 types of cells are not at all conspicuous in the vesicle stage, and were 

 it not for the more striking discrepancies which appear later, would not 

 warrant a separate treatment of the two. We have seen that during the 

 growth period some of the cells remain connected to each other by the 

 persistence of the spindle remnants, even up to the time when the vesicle 

 is fully formed. The cells which remain thus united in pairs develop into 

 the large type of spermatocyte. They are always drawn out in the form of 

 two cones with bases in contact and apices directed toward the opposite 

 ends of the follicle, — i. e. they are arranged with their longest axes 

 parallel to that of the follicle. The cell membrane separating the two 

 individuals of a pair is not nearly so well developed as that surrounding 

 the rest of the cell, and it shows more plainly its reticular character. It 

 appears to be only a very slightly modified and condensed form of cyto- 

 plasm. Furthermore, as I have said, there is a well-defined opening in 

 this part of the cell membrane through which the interzonal filaments 

 extend. This sheaf of persisting filaments is continuous in each cell 

 with the mantle of archoplasm surrounding the nucleus and is itself sur- 

 rounded by masses of archoplasm, the characteristic fibrillar structure 

 often being so masked as to be apparently obliterated. The archoplasm 

 has the form of a mantle completely enveloping the nucleus, and is dif- 

 ferentiated into two fairly well-defined layers, an outer, more dense layer 

 and an inner one, which differs only a little from the ordinary cytoplasm. 

 Both of these layers are reticular and enclose in their meshes accumula- 

 tions of very fine granules, which are more noticeable in the outer than 

 in the inner portion. In addition to these archoplastnic masses there is 

 another accumulation of a purely granular nature, which encloses the 

 two deeply staining centrosomes. 



