342 ROBERT H. BOWEN. 



and its formed elements strictly regular as regards the quanti- 

 ties involved? (2) If so, what is the mechanism for achieving 

 such a result? 



For an answer to these questions we can have recourse to no 

 more suitable material than is offered by the two spermatocyte 

 divisions. In these cases, if anywhere, we should expect to 

 find conclusive evidence of an exact regularity in division, for 

 the spermatocyte divisions and the subsequent differentiation of 

 the sperm are accomplished so rapidly that there is little time for 

 the correction of inequalities in division by differential growth. 



As a matter of fact the mass distribution of the cytoplasmic 

 elements has been studied by many workers with very uniform 

 results. Attention has thus far been centered chiefly on the mito- 

 chondria, and Duesberg ('10) has well summarized this aspect 

 of the question, showing conclusively that the spermatids arising 

 from a given spermatocyte contain each a fourth part of its orig- 

 inal mitochondrial content. This general conclusion is corrobo- 

 rated with the greatest clearness by the case of the scorpion Cen- 

 trums described by Wilson ('16) in which each spermatid re- 

 ceives accurately equal portions of a remarkable chondriosome- 

 ring characteristic of the primary spermatocytes. To be sure, 

 in another scorpion, Opisthacanthus, the distribution is some- 

 times demonstrably uneven, but the discrepancies are always 

 slight. My own observations on the Hemiptera show that the 

 mitochondria are rather accurately halved at each maturation 

 division, with the result that each spermatid receives an approxi- 

 mately equal mass of chondriosome material. On the other hand 

 there are cases in which the distribution is markedly unequal, 

 especially in forms in which the spermatocyte divisions are ab- 

 normal, as for example the honey-bee (Mfeves, '07). Of even 

 greater interest are the inequalities in the mass distribution of 

 the mitochondria in the segmenting eggs of the ascidian (Dues- 

 berg, '15). It is clear, therefore, that the division of the mito- 

 chondria considered merely from the standpoint of the quantities 

 involved is very often equal, but in certain special cases quite the 

 contrary. In any particular case, however, the distribution ap- 

 pears to be always approximately the same. In other words, 

 there is a definite regularity in the amount of mitochondria dis- 

 tributed to a given cell. 



