178 ON GENERATION. 



general congeries of smaller ones, in order that it may the more 

 readily find space to grow. Fabricius, therefore, is right when 

 he says, 1 " The yelks which are on the surface of the cluster 

 are larger than those of the middle, which are surrounded as it 

 were by the larger ones. The very smallest of all the ova are 

 situated towards the centre." That is to say, those that grow 

 acquire larger dimensions and become detached from the rest, 

 and as this proceeds, the several yelks, besides their tunica 

 propria, are invested with another from the ovary, which em- 

 braces them externally, and connects them with the base whence 

 they spring. This coat is, therefore, entitled the peduncle by 

 Fabricius, and its office is that of a foot-stalk, viz. to supply 

 nourishment to the ovum, in the same way as fruit is nourished 

 through the stalk by which it is connected with the tree. " For 

 this peduncle is a hollow membranous bond of union, extending 

 from the foundation of the cluster [the stroma of the ovary] to 

 the yelk, coming into contact with which, it is dilated and ex- 

 panded in the same way as the optic nerve in the eye, and covers 

 the vitellus with an external tunic. This perchance was what 

 Aristotle called the aroXov o/t^aXow'Srrv, or umbilical appendix, 

 and described as forming a kind of tube. This peduncle in- 

 cludes numerous vessels, which are distributed on all sides 

 around the yelk. 



So much is accurately related by Fabricius ; but he errs when 

 he says, " This tunic does not surround the entire vitellus, but 

 only extends upon it a little beyond the middle, very much in 

 the manner of an acorn within its cup ; whence it comes that 

 the outer portion of the yelk, which is not invested by the 

 membrane in question, presents itself free from vessels, and to 

 appearance naked." The membrane, nevertheless, surrounds 

 the yelk completely; but on the outer aspect it is not very easily 

 distinguished from the tunica propria, both of them being of 

 extreme delicacy. Posteriorly, however, and where the yelk is 

 turned towards the basis of the cluster, the tunic in question 

 does not adhere to the vitellus, neither does it send any vessels 

 to this part, but merely embraces it in the manner of a sac. 



Each vitellus receives a distinct tunic from the ovarian basis ; 

 whence this is not to be regarded as the common uterus, since 



1 Op. cit. p. 3. 



