STRUCTURE AND DEVELOPMENT OF VERTEBRATE OVARV. 411 



owing to the presence of certain delicate granular (in hardened 

 speciaiens)bodies, whose nature I do not understand, and to special 

 yoke spheres rather larger than the ordinary, provided with 

 numerous smaller spherules in their interior, which are probably 

 destined in the course of time to become free and to form 

 ordinary yolk spheres. 



The mode of formation of the yolk spheres above described, 

 appears to me to be the normal, and possibly the only one. Cer- 

 tain peculiar structures have, however, come under my notice, which 

 may perhaps be connected with the formation of the yolk. One 

 of these resembles the bodies described by Eiraer^ as " Dotter- 

 schorfe." I have only met these bodies in a single instance in ova 

 of ^"6 mm., from the ovary (in active growth) of a specimen of 

 Scf/. canicula 23 inches in length. In this instance they con- 

 sisted of homogeneous clear bodies (not bounded by any mem- 

 brane) of somewhat irregular shape, though usually more or less 

 oval, and rarely more than 0*02 mm. in their longest diameter. 

 They were very numerous in the peripheral laver of the ovum, 

 but quite absent in the centre, and also not found outside the 

 ovum (as they appear to be in Reptilia). Yolk granules formed 

 in the normal way, and staining deeply by os^mic acid, were 

 present, but the " Dotterschorfe " presented a marked contrast 

 to the remainder of the ovum, in being absolutely unstained by 

 osmic acid, and indeed they appeared more like a modified form of 

 vacuole than any definite body. Their general appearance in 

 Scyllium may be gathered from Eimer^s figure 8, PI. XI, though 

 they were much more numerous than represented in that figure, 

 and confined to the periphery of the ovum. 



Dr. Eimer describes a much earlier condition of these structures, 

 in which they form a clear shell enclosing a central dark nucleus. 

 This stage I have not met with, nor can I see any grounds for 

 connecting these bodies with the formation of the yolk, and the 

 fact of their not staining with osmic acid is strongly opposed 

 to this view of their function. Dr. Eimer does not appear to me 

 to bring forward any satisfactory proof that they are in any way 

 related to the formation of the yolk, but wishes to connect 

 them with the pecuHar body, well known as the yolk nucleus, 

 which is found in the amphibian ovum.'^ 



Another peculiar body found in the ova may be mentioned 

 here, though it more probably belongs to the germinal vesicle 

 than to the yolk. It has only been met within the vitellus of some 

 of the medium sized ova of a young female. Examples of this 

 •body are represented on PI. XVIII, fig. 25. A x). As a rule there 



' " Uutersuching iiber die Eier d. Reptilian," 'Archiv. f. mikros. Anat.,' 

 vol. viii. 



' Vide Allen Thomson, article "Ovum," Todd's 'Encyclopaedia,' p. 95. 



