THE OVARIES 25 



In regard to the influence of the corpus luteum on The influence 

 the implantation and subsequent growth of the ovum the corpus 

 evidence is conflicting. There is, however, no doubt i^pi^tation 6 

 that in most, if not in all, mammals higher in the scale of the ovum. 

 of evolution that the marsupials, the life of the corpus 

 luteum is prolonged in pregnancy, whether it be that 

 the corpus luteum undergoes hyperplasia to assist 

 implantation, or because of implantation. 



I have studied the question from a morphological Corpus 

 standpoint, for this method of investigation seemed morph 1 -' 

 likerv to offer some solution of many of the difficulties °J°gfcai 



J J studies. 



in regard to the corpus luteum. 



The Ornithorhynchus, in which the young is born in 

 an egg, and consequently is never attached to the 

 mother, has a somewhat remarkable corpus luteum. I 

 have not seen a very recent one, but in those in the 

 specimens examined there is an enormous deposit of 

 fibrous tissue around what appear to be lutein cells (fig. 4). 

 Ultimately the whole becomes a ball of fibrous tissue 

 (fig. 5). This arrangement does not seem at all favour- 

 able to the absorption of secretion from the lutein cells. 



In marsupials the attachment of the ovum is most 

 primitive, and one would expect to find a correspondingly 

 unimportant corpus luteum. But this expectation is 

 not borne out by facts, although Fraenkel and Cohn 1 

 must have jumped to the conclusion mentioned, for 

 they state that the corpus luteum in the marsupial is, 

 like that seen in the monotreme (Ornithorhynchus), 

 rudimentary. O'Donoghue 2 , however, has carefully 

 described the corpora lutea in several varieties of mar- 

 supials, and has shown that they are highly-developed 

 structures. That this is so will be obvious from an 

 inspection of figure 6, in which a fully-developed corpus 

 luteum in the ovary of a marsupial (Perameles obesula) 

 is seen to occupy a considerable portion of the organ, 

 and to be composed of large cells of an epithelial type. 

 If the importance of the corpus luteum increased with 



1 Fraenkel, L., and F. Cohn, Anat. Am., 1902, vol. xx, p. 294. 

 * O'Donoghue, C. H., Archiv. f. Mikr.Anat., 1914, vol.lxxxiv, p. 1. 



