302 CALKINS. 



EXPLANATION OF PLATE XIX. 



Fig. 34. Spermatid, showing reticulated nucleus and minute archoplasm mass 

 due to the killing agent. 



Fig. 35. Spermatid highly magnified, showing homogeneous nucleus becoming 

 drawn out, tail forming from cytoplasm, and with a clear space around the chro- 

 matin. Archoplasm clear and distinct. 



Fig. 36. Spermatids on blastophore, chromatin not homogeneous, archoplasm 

 minute (like a centrosome), cytoplasm more or less distorted, all due to the 

 killing agent. 



Fig. 11. Spermatid much elongated and detached from the blastophore, show- 

 ing homogeneous nucleus with a comparatively large vesicle at the extremity 

 which contains the archoplasm mass. 



Fig. 38. Spermatid. The vesicle has here disappeared ; the archoplasm now 

 connects the tail and nucleus and is the middle-piece. 



Figs. 39, 40, 41, and 42. Spermatocytes of the first order, showing different 

 stages in the history of the archoplasm. 



Fig. 43. Spermatosphere in the spermatocyte stage, showing archoplasm 

 masses extending up the spindle fibres. The fibres come from the archoplasm. 



Fig. 43A. Spermatid in the anaphase of karyokinesis, showing withdrawal of 

 the spindle fibres into the archoplasm mass. 



Figs. 44 and 46. Artefacts, showing the protrusion of nucleoli. 



Fig. 45. Spermatocytes of the first order, showing central spindle between the 

 divided archoplasm masses. Nebenkern is also present. 



Fig. 47. Late spermatozoon, showing tail, middle-piece, and head, also the 

 spur (S) formed from the point of cytoplasm by which the spermatid had been 

 attached to the blastophore. 



