34 WALTER HE APE. 



The vesicle contains a transparent fluid, the nature of which 

 I am only sufficiently conversant with to say that, after treat- 

 ment with alcohol a white precipitate is present in the vesicle. 



It is equally evident that this fluid can only have been 

 obtained from the uterus, and that it is present within the 

 vesicle at a very considerably greater pressure than in the 

 uterus itself. Such a condition is caused by means of the cells 

 of the wall of the vesicle ; they secrete the fluid within the 

 vesicle, this function being performed against a pressure which 

 is greater on their inner than on their outer side, exactly as the 

 cells of the salivary glands are known to act. 



The uterine fluid is secreted by glands, present in great 

 numbers in the uterine tissue, and is poured through their open 

 mouths into the cavity of the uterus (vide fig. 51). There is 

 every probability it has nutritive qualities, since it is thence 

 taken up into the cavity of the embryonic vesicle, which 

 eventually functions as a yolk-sac, in the walls of which em- 

 bryonic blood-vessels ramify. 



A specimen showing an early condition of this change of the 

 segmented ovum into a vesicle has been drawn in optical section 

 in fig. 2. It differs mainly from fig. 1 in that a crescent-shaped 

 cavity (jbl. cav.) exists between the inner mass and outer layer, 

 this being the cavity of the blastodermic vesicle. 



Van Beneden's blastopore has entirely disappeared, and I have 

 no evidence to offer as to the position which it originally occu- 

 pied ; although there is good reason to believe, from a comparison 

 of the development of the rabbit and mole with animals which 

 exhibit the phenomena attending the inversion of the layers, 

 that Beneden's statement is correct, viz. that the inner mass 

 remains attached to that side of the outer layer where the gap 

 was originally placed. 



The appearance of the cells has altered but little ; the outer 

 layer cells are slightly more granular, while the cells of the 

 inner mass are somewhat smaller and less granular than were 

 those of the fully-segmented ovum. 



The size of the two ova are different, the specimen from which 



