SPERMAfOGETSTESIS OF STENOBOTHRUS VIRIDULUS. 15 



The torpedo-shaped spermatids are to be seen scattered in the follicle^ and 

 are very prominent objects on account of the strong staining of the iron 

 hsematoxylin : they are placed usually with their heads towards the anterior 

 end of the follicle, and travel as unripe spermatozoa, tail first, towards the 

 posterior end. As they elongate further into the thin thread-like form 

 characteristic of the unripe spermatozoa, they become associated in ragged 

 clusters, which continue to condense until we find solid masses of ripe and 

 finely drawn out spermatozoa situate at irregular intervals in the lumen of 

 the follicle. Plate 3. fig. 36 shows the penultimate stage immediately 

 preceding the transformation into the mature spermatozoon, and is a good 

 example of the much reduced " centrosome " and the darkly staining and 

 considerably elongated nucleus. 



Summary. 



1. The apical cell is found at the extreme anterior end of the mature 

 follicle, completely surrounded by a single layer of primary spermatogonial 

 cells. There is only one apical cell in each follicle. 



2. The secondary spermatogonia occur in clusters and morphologically 

 appear similar to the primary cells, but are recognizable by the absence of 

 the apical cell and by the number of clusters. 



3. The nucleus exhibits an apparently complete reticulum in the resting- 

 stages of both primary and secondary spermatogonia : there is no trace of 

 the identity of either heterotropic or ordinary chromosomes. 



4. The chromosomes of the spermatogonial complex can be arranged in 

 a graduated series of pairs, and are divisible into three groups, viz., large^ 

 small, and medium-sized chromosomes. The number of chromosomes is 

 constant and is seventeen, the fourth largest being unpaired and corresponding 

 with the " monosome " and " accessory " chromosome of other writers. 



5. All the members of the spermatogonial complex divide in mitosis ; but 

 the odd or heterotropic chromosome often " lags," and can be seen on the 

 spindle when the ordinary chromosomes are assembling at the poles. 



6. The nucleus is at its smallest size after the last spermatogonial division, 

 and this stage is followed by a clearly observable growth-period, extending 

 to the prophase of the first maturation division. In this resting-stage the 

 nucleus again exhibits a chrom.atin reticulum, the granules being disposed 

 along linin threads : the identity of the ordinary chromosomes is lost, but 

 the heterotropic chromosome remains as a dark and homogeneous body close 

 to the periphery of the nucleus, and undergoes no resolution into a spireme. 



7. I have found no trace of separate sacs or vesicles in which chromo- 

 somes undergo transformation into spiremes, either in the case of the hetero- 

 tropic or the ordinary chromosomes. 



8. The equatorial plate of the primary spermatocyte mitosis shows nine 



