132 J- Moore, 



cats, rabbits, mice, bulls, pigs, hedgehogs and men, the results have 

 been sufficiently uniform to allow the description to be contracted, at 

 any rate for the present, within the range of a single one. For this 

 purpose I have chosen the rat, as it is undoubtedly one of the most 

 generalized types, while, at the same time, it exhibits in their most 

 acute form, individual variations which, without a sufficiently compara- 

 tive study, might be, and indeed have been, taken as essential features. 

 When occasion calls for it and other types Seem better suited to my 

 purpose, I shall make reference to the species in question, but the great 

 mass of my descriptive matter refers entirely to the rat. 



Concerning the existence of a „Reductions-Teilung" 

 in Mammalia. 



In mammals, as is well known, the growing cells, or those which 

 are produced by the penultimate division of the spermatogenesis, and 

 which on that account might not inaptly be termed spermatocytes, arise 

 in the majority of cases by a division whose long axis is parallel to the 

 surface of the tubule. This and the succeeding final divisions are generally 

 typically mitotic, and the question naturally arises whether we are 

 justified in regarding these penultimate and final divisions as correspon- 

 ding to that of the „Reductions-Teilung" of the invertebrata. In the 

 closely co-incident descriptions of the Spermatogenesis in Diaptomus and 

 Gryllotalpa given by Ishikawa^) and vom Rath^), the number of the 

 chromosomes present in the corresponding penultimate division was 

 double that of the cells of the ordinary somatic tissues. The effect of 

 this division itself is to reduce this number back to the normal, and 

 the last one occurs, according to these authors, in precisely the same 

 manner as the „Reductions-Teilung" or pseudomitosis described by 

 0. Hertwig^) in Ascaris — i. e. by a transmigration of unsplit chro- 

 mosomes into the daughter-cells. 



The Arthropod spermatogenesis with which I am most intimatel}' 

 acquainted, (that of Branchipus) appears to correspond but partially 



') Jour. Sci. Coll. Imp. Univ. Tokio. Vol. V. p. 1—34. 

 -) Archiv für mikr. Anat. Bd. XL. p. 102—130. 

 '') Archiv für mikr. Anat. Bd. XXXVI. p. 1—127. 



