22 KARYOKINESIS. 



archoplasm.^ A spermatozoon enters the ovum almost immediately after it reaches 

 the uterus and while the germinal vesicle is still intact, fig. 3, et seq. The sperm 

 ma}' enter at any point on the surface of the egg, except within a small area im- 

 mediately surrounding the animal pole ; usually, however, it enters near the vegetal 

 pole. Polyspermy is exceedingij- rare; one sometimes finds several spermatozoa 

 attached to an egg, and in a few cases two spermatozoa may be found penetrating 

 the egg membrane or lying just Avithin it, fig. 10, but onlj^ on one or two occasions 

 have I seen two well-developed sperm nuclei within one egg. The pointed head of 

 the sjjermatozoon bores through the egg membrane, figs. 18, 19, 20, though the tail 

 does not enter. After the sperm head is well through the egg membrane several 

 granules are found just behind the head; these are probably derived from the middle 

 piece. Their number and arrangement is variable, but there are always more than 

 two, so far as I have observed, and they are never grouped at the poles of a 

 spindle. After its entrance, the head occupies such positions as to justify the belief 

 that it turns around, as is known to be the case in manj- other animals (cf. figs 18, 

 19, 20, 21). 



Foot ('94 and '97) has described in Allolobophora a number of dark round 

 bodies which stain as intensely as the sperm head itself, and which lie on each side 

 of the head or at its posterior end. These she calls the sperm granules and suggests 

 that they may be formed from metamorphosed archoplasm. They are not constant 

 in appearance and may be the result of degeneration. 



Byrnes ('99) has also observed in Livtax a number of darkly staining granules 

 which accompany the sperm head. She suggests that they are derived from particles 

 of chromatin constricted off from the sperm nucleus. Later they disappear and 

 become scattered through the cytoplasm of the egg. 



In the main the resemblance of these "sperm granules," both of Allolobopho7'a 

 and Limax, to those which I have observed in Crepidula, is striking enough. I can- 

 not believe, however, that they are degeneration products in Crepidula and for that 

 reason, among others, have not adopted Foot's name for them. 



2. The Germ Nuclei. — Immediately after the sperm head has entered the egg 

 it is seen to be a pointed rod with three constrictions and four enlargements, having 

 much the same size and shape as one of the 4-part chromosomes found in the meta- 

 phase of the first maturation division, fig. 18. It soon grows shorter and thicker 

 and becomes dumb-bell shaped, fig. 20, then nearly spherical, figs. 10, 21, and then 

 irregular or amoeboid, figs. 39, 40. Up to this stage it has remained chromatic 

 throughout, but from this time forward spaces filled with achromatic substance 

 appear within it and it begins to grow vesicular. V. Klinckowstrom ('96) and Van 

 der Stricht ('98) have observed a similar transformation of the sperm nucleus in 

 Prostheceraeus and in Thysanozoon, the sperm head being first moniliform, then 

 spherical, then vesicular. 



' Byrnes ('99) finds no middle piece in tlie spermatozoon of Limax and suggests that it may possibly 

 be surrounded or overgrown by the sperm head. 



