IV.] FOUNDATION OF A THEORY OF HEREDITY. 225 



Applying these ideas to the sperm-cells we must see whether 

 the expulsion of part of the nuclear substance, viz. of the 

 spermogenetic nucleoplasm, corresponding to the ovogenetic 

 nucleoplasm, takes place in them also. 



As far as we can judge from thoroughly substantiated observa- 

 tions such phenomena are indeed found in many cases, although 

 they appear to be different from those occurring in the egg-cell, 

 and cannot receive quite so certain an interpretation. 



The attempt to prove that a process similar to the expulsion 

 of polar bodies takes place in the formation of sperm-cells has 

 already been made by those observers who regard such ex- 

 pulsion as the removal of the male element from the egg, thus 

 leading to sexual differentiation ; for such a theory also requires 

 the removal of part of the nuclear substance from the maturing 

 sperm-cell. Thus, according to E. van Beneden and Ch. Julin, 

 the cells which, in Ascaris, produce the spermatogonia (mother- 

 cells of the sperm-cells), expel certain elements from their 

 nuclear plate, a phenomenon which has not been hitherto ob- 

 served in any other animal, and even in this instance has only 

 been inferred and not directly observed. Moreover the sperm- 

 cells have not attained their specific form (conical bullet-shaped) 

 at the time when this expulsion takes place from the sperma- 

 togonia, and we should expect that the spermogenetic nucleo- 

 plasm would not be removed until it has completed its work, 

 viz. not until the specific shape of the sperm-cell has been 

 attained. We might rather suppose that phenomena explicable 

 in this way are to be witnessed in those sperm-blastophores 

 (mother-cells of sperm-cells) which, as has been known for a 

 long time, are not employed in the formation of the nuclei of 

 sperm-cells, but for the greater part remain at the base of the 

 latter and perish after their maturation and separation. In this 

 case an influence might be exerted by these nuclei upon the 

 specific form of the sperm-cells, for the former arise and de- 

 velope in the form of bundles of spermatozoa in the interior of 

 the mother-cell. 



It has been already shown in many groups of animals that 

 parts of the sperm-mother-cells ^ perish, without developing 



1 I purposely abstain from using a more precise term, for the compli- 

 cated terminology employed in spermatogenesis hardly contributes any- 

 thing to the elucidation of the phenomena themselves. Why do we not 



