176 SUMMARY OF CURRENT RESEARCHES RELATING TO 



general views of mammalian embryology based by Robinson and otters 

 wholly or partly on bis results. In botb cases tbe points at issue are 

 difficult to make clear without figures. According to Jenkinson, Robin- 

 son's observations may be stated as follows : — Tbe blastocyst at its 

 earliest stage consists of a hollow vesicle with a one-layered roof of 

 epiblast, a many-layered floor of hypoblast, the cavity being the seg- 

 mentation cavity. Later the thin roof becomes invaginated into the 

 segmentation cavity, which is thus obliterated, and a space — the cavity 

 of the yolk-sac — is formed in the thickened hypoblast by vacuolation. 

 Jenkinson criticises these statements and the figures, and describes what 

 he regards as the true state of affairs, which is essentially that described 

 by other observers for different mammals. He then proceeds to the dis- 

 cussion of the views which have been held by different authors on the 

 problems of mammalian embryology, and gives the general results as 

 follows. It is impossible to institute homologies between the mammalian 

 blastocyst as such and the segmented ova of other Vertebrata, because 

 we have no clear idea how the mammalian ovum has been derived from 

 an amphibian or reptilian ancestor. Until lately, two separate processes 

 have been in Vertebrata confused under the term gastrulation. " The 

 first is a movement of the vegetative cells towards the animal pole, 

 inside the cells of which they may become included ; the second is a 

 backward and lateral overgrowth and ingrowth of animal cells to form a 

 notochordal and mesodermal plate, and possibly the roof of the gut on 

 the inside, and on the outside the medullary plate, which thus lies on 

 what was originally the vegetative pole of the egg." It is thus not pos- 

 sible to speak of gastrulation without knowledge of the axes of the egg ; 

 and as we do not possess this knowledge for mammalia, it is better to 

 avoid the term altogether. 



First Directive Spindle in Ovum of Mouse.* — Herr J. Sobotta 

 shows that the peculiarly large almost central spindle-figures which 

 are seen towards the end of the maturation period of the follicle, and 

 usually in the monaster stage, are the first directive spindles. More 

 frequently seen, especially in atretic follicles, are the second directive 

 spindles. In many cases, in the mouse and in other mammals, it seems 

 as if the first directive division were wholly suppressed. 



Suprarenals of Mammals. f — Dr. 0. Aichel finds that in mammals 

 up to rodents the whole mesonephros persists for a long time, and the 

 earliest rudiment of the supra-renals appears within the upper third ; 

 while in mammals from insectivores upwards, the upper third disappears 

 early. In the latter case the connection of the rudiment of the supra- 

 renals with the mesonephric funnels, discernible in the lower mammals, 

 is no longer to be seen, the organs appearing free in the mesenchyme 

 without connection with mesonephros or ccelomic epithelium or vessels. 

 The medullary substance is formed of the same blastema as the cortical 

 part, without co-operation from the sympathetic nervous system. 



Aichel distinguishes in man between the supra-renals which arise 

 from the ej)oophoron aDd paroophoron, and the supra-renals of Marchand 

 which appear casually beside the main organ, though both have their 



* Festschrift Phvs.-Med. Ges. Wiirzburg, 1899, pp. 187-92 (1 pi.). 

 t Anat. Anzeig., xvii. (1900) pp. 30-1. 



