52 CYTOPLASMIC STRUCTURES IN THE SEMINAL EPITHELIUM OF THE OPOSSUM. 



shape. The proximal centriole is inserted on the nucleus and very soon it becomes 

 apparent that this insertion is not directly in the center of the nucleus, but toward 

 one extremity ("laterale Insertion"). The distal centriole assumes the form of a 

 disc, the middle portion of which, carrying the axial filament, later breaks off, 

 leaving a ring and a small granule (distaler Centralkorperknopf). When the head 

 has assumed its definite shape one finds this granule connected with the proximal 

 centriole by a thin filament. Both are located in the notch of the head. The 

 axial filament is very thin in the region of the future middle piece, while posteriorly 

 it suddenly becomes much thicker. This part, which corresponds to the future 

 main piece, exhibits a peculiar structure, a cross striation. The protoplasmic body 

 has elongated and (contrary to what is found in many other mammals) extends 

 farther back than the middle piece. 



With the sudden disappearance of the caudal tube the third period begins. 

 Most remarkable is the fate of the headcap, which is left by the spermatozoon in 

 the protoplasm of the Sertoli cell. The centriolar ring migrates to the end of the 

 middle piece, while the proximal centriole breaks into two granules connected by 

 a thin filament with each other and with the granular part of the distal centriole. 

 The chondriosomes dispose themselves around the axial filament. Finally, most of 

 the protoplasm, with the so-called von Ebner's "tingierbare Korner," is eliminated. 



A striking change occurs during the fourth period, a change in the position of 

 the head in relation to the tail. At first the axis of the head was at right angles 

 with that of the tail, but in spermatozoa collected in the epididymis the head is 

 found in the same long axis with the tail. 



From this short summary it appears that the process is similar to what is 

 observed in other mammals, the modifications of the centrioles, compared with those 

 which occur in the guinea-pig, belonging to a rather simple type. The most striking 

 feature of the process is the elimination of the headcap from the spermatozoon. 1 



While it appeared necessary to give a summary of von Korff 's paper on account 

 of the marked resemblance between his description and my own findings, and 

 because of the close relationship between the species investigated, it is not my 

 intention to review again the whole Literature relating to spermiogenesis in mam- 

 mals. I refer the reader to my paper of 1908, and will Limit myself to an account 

 of two papers which have appeared since and which are concerned with the process 

 of spermiogenesis, or certain phases of it in mammals one by Oliver (1913) on 

 spermiogenesis in the fur seal, the other by Stockard and Papanicolaou (1916) on 

 the modifications of the idiozome in the guinea-pig. 2 



Oliver's conclusions agree in the main with those of Meves (1899), von Ivorff 

 (1902), and the author (1908). There is, however, one point of difference. While 

 Oliver admits, rightly in my opinion, the formation of the caudal tube at the 

 expense of cytoplasmic material here, as in the guinea-pig (Meves, 1899) its 

 formation from filaments is quite apparent in opposition to Meves, myself, and a 



'A paper by Benda (1906) on spermatogenesis in marsupials was not available in this country. I can therefore only 

 quote from my own former references to it (1908, 10112). 



- E. Allen's "Studies on pell-division in the albino rat III" (Journ. of Morph., vol. 31, 1918), appeared too late for 

 discussion here, but I should like to warn the reader that practically wherever I am quoted in that paper such quotations 

 are inaccurate. 



