in the Cyclopcedia of Physiology. 285 



originally single spot. (Thus the germ vesicle is formed out of 

 what in A was a nucleolus, and in B had become a nucleus.) In 

 figs. E and F, h is the ovisac, or rather the foundation of its 

 membrane. In fig. E, g represents the granular contents of a 

 future cell — the ovisac. They are part of the nucleus, fig. A. 

 Out of these granular contents [g, fig. E) are formed the albu- 

 nienous contents of the ovisac, including von Baer^s membrana 

 granulosa and my retinacula, as well as the yelk and vitelline 

 membrane*. 



From my observations then it appears that the ovisac and all 

 within it are formed out of a nucleus — fig. A ; that the ovisac is 

 the cell, and that the germ vesicle is what was once a nucleolus. 

 This nucleolus (young germ vesicle) often divides into two or 

 more parts, and then the ovisac comes to include a plurality of 

 ova; for a yelk forms around each part of the divided nucleolus. 



Besides what has now been mentioned, the said article 

 ''Ovum^' in the Cyclopaedia of Physiology adds yet another proof 

 to many in my experience, that it is often unfortunate for an 

 observer to have the exploring of new ground. His observations 

 may remain so long disregarded or denied, that when at length, 

 after the lapse of no small fraction of a century, they come to 

 be confirmed, he has the pain of exhuming them, all remem- 

 brance thereof being gone. I have had large experience of this, 

 and am now compelled to endure the pain of more. 



Thus Prof. Allen Thomson was certainly not aware of what I 

 had recorded in 1 839, or he would not have considered altogether 

 " novel '' some views published in Germany in 1852. 



H. Meckel, 1852 — as j-eported 

 in the article " Ovum,'^ 1834. 



*' Many physiologists have felt the 

 incongruity of the comparison gene- 

 rally made between the minute and 

 simple ovum of the mammifer, and 

 the large and more complex yolk of 

 the bird, and most are disposed to 

 acknowledge the necessity of making 

 some more markeddistinctionbetween 

 the granular and the cellular yolk 

 substance in the two great groups 

 to which these ova respectively 

 belong. It has before been stated, 

 that von Baer, on his discovery of 

 the mamraiferous ovum, regarded it 

 as corresponding, not to the whole 



Martin Barry, 

 Phil. Trans. 1839. 



After showing that cleavage, so 

 called, takes place in the ovum of 

 the highest class, Mammalia, I re- 

 marked : " In Fishes the divisions in 

 question do not include the whole 

 yelk-ball, but are confined to a pro- 

 jection on one side. In the Frog 

 those divisions include the whole of 

 the yelk-ball, but they begin and 

 proceed more vigorously on one 

 side. In Mammalia also, as we have 

 seen, the divisions include the w hole 

 of the so-called 'yelk-ball.' This 

 comparison may perhaps assist us in 

 determining what portion it is of the 



* The said drawings A to E represent the young ovum and ovisac of a 

 Bird — the Wryneck, Yunx torquilla. In ¥ is part of a young ovisac of the 

 Canary, Vringilla Canaria. 



