FOUNDATION OF A THEORY OF HEREDITY. 221 



expel certain elements from their nuclear plate, a phenomenon which 

 has not been hitherto observed 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 spermatogonia, and we should expect that the spermo- 

 genetic nucleoplasm 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 explic- 

 able 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 in- 

 fluence might be exerted by these nuclei upon the specific form of 

 the sperm-cells, for the former arise and develope 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 1 perish, without developing into sperm- 

 cells, as in Selachians, in the frog, in many worms and snails, 

 and also in mammals (Blomfield). But the attention of observers 

 has been directed to that part of the cell-body which is not used 

 in the formation of sperm-cells, rather than to the nucleus ; and 

 the proof that part of the nucleus also perishes is still wanting 

 in many of these cases. Fresh investigation must decide whether 

 the nucleus of the sperm-mother-cell perishes as a general rule, 

 and whether part of the nucleus is rendered powerless in some 

 other way, where such mother-cells do not exist. Perhaps the 

 paranucleus (Nebenkern) of the sperm-cell, first described by La 

 Valette St. George, and afterwards found in many animals of very 

 different groups, is the analogue of the polar body. It is true that 

 this so-called paranucleus is now considered as a condensed part of 



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

 minology employed in spermatogenesis hardly contributes anything to the elucida- 

 tion of the phenomena themselves. Why do we not simply speak of sperm-cells 

 and spermatoblasts, and distinguish the latter by numbers when they occur in 

 successive generations of different form? Moreover, all the names which have been 

 suggested for successive stages of development, can only be applied to the special 

 group of animals upon which the observations have been made. Hence great con- 

 fusion results from the use of such terms as spermatoblasts, spermatogonia, sperma- 

 tomeres, spermatooysts, spermatocytes, spermatogemmae, etc. 



