No. I.] THE EGG OF LIMAX AGRESTIS. 21 I 



in the middle of the centrosphere of the archiamphiaster (cf. 

 PI. XII, Fig. 25, with PL XI, Fig. 3). The rays of the spiral 

 aster continue to lengthen, so that the entire cytoplasm is now 

 involved in the formation of a spiral, which extends from the 

 egg-astrosphaere as a center to the circumference of the egg 

 (PL XII, Fig. 22). PL XII, Fig, 23, shows a section taken 

 through the spiral aster near the equator of the q^^. It also 

 shows that the rays are bent so as to form a right-handed 

 spiral. 



The third period is the period of the disappearance of the 

 egg-astrosphaere. The central body, or centrosome (PL XII, 

 I^'jg- 25), gradually fades away (PL XII, Figs. 26 and 27) and 

 gives place to a reticulum which traverses the entire sphaere 

 (PL XII, Fig. 28). In this stage the centrosphere corresponds 

 exactly to the reticulated centrosphere figured by Wilson for 

 Toxopneustes,^ and by Brauer for Artemia salina. During the 

 third period the spiral aster is still plainly visible, but it is less 

 distinct than during the second period. As the nucleus enlarges 

 it gradually encroaches on the reticulated centrosphere, and 

 finally comes to occupy the entire site of the sphaere, so that 

 the astral rays now seem to diverge directly from the periphery 

 of the nucleus as a center (PL XII, Fig. 31). The rays become 

 more and more vague, until they disappear and nothing remains 

 of the egg-astrosphaere. The maturation of the ovum is now 

 complete. 



II. Structure and Maturation of the Spermatozoon. 



I. Structure of the Spermatozoon. 



The spermatozoa were mounted whole on the slide, and killed 

 in a. yi per cent solution of acetic acid, and also in a saturated 

 solution of corrosive sublimate to which 5 per cent acetic acid 

 was added. They were then stained with Heidenhain's iron- 

 haematoxylin and with various double stains, such as Lyons 

 blue and borax-carmine, iron-haematoxylin and orange G., acid 

 green and eosin, eosin and haematoxylin. After all of these 



1 Diagram J^, Fig. 108, in "The Cell," WDson. 



