42 EMBRYOLOGY. 



the male seminal elements ordinarily present in the animal kingdom: 

 for they are apparently motionless ; are comparable in form to a cone, 

 a conical ball, cr a thimble (fig. 21) ; and consist in part of a 

 granular substance (b), in part of a homogeneous lustrous substance 

 (/), and of a small spherical body of nuclear substance (/), which is 

 imbedded in the granular substance at the base of the cone. 



When the small naked eggs enter into the region designated as 

 uterus, fertilisation takes place at once. One spermatic body, which 

 can execute feeble amoeboid motions with its basal end (SCHNEIDER), 

 attaches itself to the surface of the yolk (fig. 22 sk). Where contact 

 with the egg first takes place, there is formed, exactly as in the 

 Echinoderms, a special cone of attraction. Here the spermatic 



body, without essential change of form, gradually 



glides deeper into the yolk, until it is completely 



enclosed therein (fig. 23). 



While the two sexual products are thus externally 



fused, the egg itself is not yet ripe, because it still 

 Fig. 21. Spermatic possesses the germinative vesicle (fig. 22 kb), but 



body of Ascaris , 



megalocephaia, " novv promptly begins to enter upon the matura- 



after VAN BENE- tion stage by preparing to form the polar cells. 



k, Nucleus ; 6, base The germinative vesicle, which is of small size in 



of the cone by the case of the Maw-worm of the Horse, loses its 



which the attach 



ment to the egg sharp delimitation from the yolk, moves toward 

 takes place; /, ^hat surface of the egg which is opposite to the 



lustrous substance . x x 



resembling fat. cone of attraction (figs. 23, 24), and is gradually 



converted into a nuclear spindle (sp), the origin 

 of which may be traced upon this object with considerable precision. 

 The most important part of the process consists in the formation, 

 out of the chromatic substance, of numerous short, rod-like pieces 

 (figs. 23, 24, ch), which form directly the chromatic elements of 

 the spindle, the chromosomes (WALDEYER). As in the case of the 

 Echinoderms, there then arise at the surface of the yolk two small 

 polar cells (fig. 25 pz) ; as in that case, a vesicular egg nucleus 

 (fig. 25 ei) arises from the half of the second polar spindle which 

 remains in the peripheral portion of the yolk. 



Meanwhile the spermatic body has moved farther and farther 

 from the place of its entrance into the egg (figs. 22, 23, sk), and 

 finally comes to lie in the middle of the yolk (fig. 24 sk), approxi- 

 mately in the position occupied by the germinative vesicle before its 

 migration to the surface. During this period the spermatic body 

 has gradually lost its original form and its sharp delimitation ; out 



