2O2 C. M. CHILD. 



deeply as the granules themselves but this is very likely due to its 

 smaller diameter. 



The next step is the formation of the tail which appears first 

 as a delicate thread extending from the granule at the border of 

 the cytoplasm (Fig. 46, PL XIV.). 



Figs. 47, AAr7, (PL XIV.) show the developing spermato- 

 zoa after different methods of fixation and staining : Fig. 47, A, 

 is from M. expansa after sublimate and Delafield's haematoxylin ; 

 Fig. 47, B, M. expansa after sublimate and iron-haematoxylin ; 

 Fig. 47, C, M. planissima, after chrom-oxalic and iron-haema- 

 toxylin ; Fig. 47, D, M. expansa, after Hermann and iron-hasma- 

 toxylin. Fig. 47, E, is from M. planissima after sublimate and 

 iron-haematoxylin, but with extraction stopped at an earlier 

 stage. One interesting point in this figure as compared with the 

 others is the much larger size of the peripheral cytoplasmic gran- 

 ule and the fiber connecting it with the nucleus --an excellent 

 illustration of the uncertainty attending the use of iron- 

 haematoxylin. 



The tail of the spermatozoon grows to a very great length. 

 Fresh spermatozoa obtained by teasing living proglottids in indif- 

 ferent fluids are 0.3-0.4 mm. in length. Most or all the tails aris- 

 ing from one cytophore usually lie parallel in the testis, and 

 since their length is much greater than the diameter of the testis 

 they become coiled in the spaces between the cells or along the 

 wall of the testis. The tail is very delicate and without visible 

 differentiation in structure. 



As regards the formation of the head of the spermatozoon 

 Moniezia does not seem to agree with other species described. At 

 least I know of no other case in which the sperm-head, if it can 

 be called a head, is formed in the manner described below. 



In my study of spermatogenesis I was for a long time puzzled 

 by the fact that all of the sperm nuclei appeared to degenerate 

 after the tails were formed. Masses like Fig. 49 (PL XV.) 

 consisting of degenerating nuclei and condensed cytophore cyto- 

 plasm can be found in every older testis. At first I concluded 

 that these were probably the spermatids formed by fragmenta- 

 tion which began the development of spermatozoa but were un- 

 able to complete it. But another feature made the matter still 



