282 CALKINS. [Vol. XI. 



cylindrical, with rounded ends (Figs. 35 and 36). At the same 

 time the beginning of the tail appears as a minute pointed 

 prominence of cytoplasm immediately above the archoplasm at 

 the distal extremity of the cell (Fig. 6). As the elongation 

 continues the chromatin portion becomes longer and thinner. 

 In chromic acid preparations it still retains its reticulated 

 appearance (Fig. 36), but after Hermann's fluid it is more 

 dense and compact (Fig. 35), and ends distally in the growing 

 tail filament. The archoplasm, which in some cases is drawn 

 out distally, lies in the triangular area at the base of the tail, 

 and, at a later stage, a large vesicle is formed about it (Fig. 37, V) 

 which is typical of the spermatid at this time. The further 

 history is briefly as follows : the nucleus and tail elongate still 

 more ; the vesicle disappears by elongation of the archoplasm 

 mass, and the head of the spermatozoon finally assumes the 

 shape of a long rod with a much longer filamentous tail. 



The cytoplasm is apparently stretched to its utmost, for only 

 the most careful observations on favorable preparations will 

 reveal it lying as a mere line around the nucleus and middle- 

 piece (Fig. 37). The young spermatozoon now consists of a 

 filament composed of three parts. First : the nucleus or head, 

 which is directed towards and seems to be attached to the 

 blastophore, but which is in reality separated from it by a small 

 amount of cytoplasm (Figs. 37 and 38 j-). Second : the middle- 

 piece, which appears as a direct continuation of the nucleus so 

 that it can be distinguished only after differential staining 

 (Figs. 38 and 47 m). Third : the tail or flagellum, which is 

 much longer than the nucleus and much finer. The small 

 amount of protoplasm between the head of the spermatozoon 

 and the blastophore becomes drawn out into a sharp spur after 

 the cell breaks away (Fig. 47 s), and this, according to the 

 observations of Foot ('94), acts as a boring-point with which the 

 spermatozoon pierces the Q.^g. 



IV. Archoplasm. 



The spermatogenesis of Lumbricus offers exceptional advan- 

 tages for the study of archoplasm, which forms a conspicuous 



