358 SUMMARY OF CUREENT RESEARCHES RELATING TO 



plasm constantly increase in size, and the spermatocytes seem to be 

 undergoing division ; the later stages of the development of the 

 spermatozoon are marked by the increase in number and fusion of 

 the large refractive bodies, which, at first small and hard to count, 

 end by forming a highly refractive body. As is well known, the 

 spermatozoa of the Nematoids are not provided with a single tail ; 

 there are rather long, pseudopodioid tentacles, which are, at the body 

 temperature of the host, actively mobile, and which consist of a hyaline 

 ground-substance with finely granular deposits. 



The only point of resemblance in the modes of development of 

 the ova and spermatozoa (after, of course, the very earliest stages) lies 

 in the fact that both kinds of genital products are disposed radially 

 around a central rachis. The germinal vesicle becomes irregular in 

 form, as the ovarian tube increases in thickness ; the germinal spots 

 become grouped into two or three grains, which, later on, undergo 

 various changes, whether the egg is fertilized or not. If the ova are 

 treated with acetic acid or with a mixture of alcohol and ether, so as 

 to extract the contained spheres and crystals, a trabecular structure is 

 to be detected ; this is of some importance, as it explains the decrease 

 in the size of the yolk after fertilization. 



As a result of a large number of observations, Nussbaum states 

 that only one spermatozoon enters each ovum ; the egg becomes smooth 

 in contour, but at the point where the spermatozoon had entered the 

 ovum is a little swollen ; the changes undergone by the male element 

 are fully described. 



As soon as the ovarian and spermatic nuclei have united, cleavage 

 commences. The colourable substance of the nucleus becomes 

 arranged in filaments which gradually thicken and diminish in 

 number. The ordinary spindle-shaped figure appears, and four chief 

 filaments are to be made out. At the poles of the spindles there is a 

 distinct radiation in the protoplasm. In these animals a large number 

 of ova are never fertilized. 



The theory of fertilization is next considered under the several 

 heads of the entrance of the spermatozoa and their changes within 

 the egg, the formation of the polar globules, and the appearance of 

 the two nuclei in the fertilized ovum. The conclusion is arrived 

 at that the act of fertilization in the simplest and in the most com- 

 plicated organisms consists in the union of the identical parts of two 

 homologous cells. 



The inheritance of individual or transmitted peculiarities is 

 regarded as being due to the influences exerted on the generative 

 cells of the individual, for they are subjected to conditions which had 

 a modifying influence on the ancestral organism. 



The author finally discusses the part played by the different por- 

 tions of the seminal cell, and comes to the following conclusions : — 



The nucleus of every seminal cell is thickened, and is in all 

 cases retained by the mature seminal body ; in spermatic filaments it 

 forms the head. During impregnation of the ovum, the modified 

 nucleus fuses with the ovarian nucleus. The protoplasm of the 

 seminal cell forms the covering of the " head," the median portion, 



