474 On the Transmission of Hereditary Gharacters. 



proved it would be premature to enter into a discussion as to 

 what is the primum movens in the fission of the Infusoria. 

 I have, liowever, really no doubt that sooner or later corre- 

 sponding structures will be found in these forms also. 



Until quite recently great uncertainty prevailed as to the 

 origin of the polar bodies or centrosomata in the fertilized 

 ovum. Many authors made no precise statements at all on 

 the point. Boveri's hypothesis, according to which they arise 

 from the protoplasm of the spermatozoon, has already been 

 alluded to. This year this deficiency in our knowledge was 

 supplied by the new investigations of Fol upon the ova of 

 Echinids, and thus the last vestige of foundation was with- 

 drawn from the theory that the nuclei are the sole vehicles of 

 heredity. Fol's memoir marks, so to speak, the last stage in 

 the present purely morphological knowledge of the process of 

 fertilization. The investigator alluded to examined the ferti- 

 lized ova of Echinids (as also those of other types) by means 

 of thin sections, with the following results : — On the pene- 

 tration of the spermatozoon into the ovum, its tip separates 

 from it, and forms the " spermocenlrum " (the polar body 

 which precedes the male pronucleus) ; this, as well as the 

 " ovocentrum," which was pre-existent in the ovum beside 

 the female pronucleus, having arisen from the directive aniphi- 

 aster, elongates into a dumb-bell shape, when the pronuclei 

 have come together*, and undergoes division. A migration 

 of the halves resulting from the fission now takes place, in 

 such a way that each half of the spermocentrum finally comes 

 into contact with a half of the ovocentrum and fuses with it. 

 The bodies which are thus constituted, each of which con- 

 sists of a male and female half, are the polar bodies or centro- 

 somata (" astrocentres " of Fol) of the first segmentation 

 amphiaster. For the present these are the only conclusions 

 which Fol deduces from his investigations : — '' Fertilization 

 consists, not merely in the aggregation of two pronuclei, which 

 proceed from individuals of different sexes, but also at the 

 same time in the union of two pairs of half-centres (' Halb- 

 ceutren '), of which one unit is derived from the father and 

 the other from the mother, to form two new bodies — the 

 astrocentres. Since all the astrocentres in an individual 

 presumably originate through fission from the two centres of 

 the first amphiaster, they all proceed in equal portions from 

 the father and the mother." 



Now if anyone, on the basis of these results, were to main- 

 tain, in an assemblage of zoologists, that the centrosomata 



* Fol agrees with van Beneden in stating that in the normal course 

 no fusion of the pronuclei takes place. 



