540 E. V. COWDRY 



For example, Aime ('07) attempted to classify the mammals into 

 groups on the basis of the occurrence of interstitial cells in their ovaries. 

 He recognized four. In the first (Solipedes) he believed them to occur 

 only in fetal life; in the second (bats, insectivors and rodents), only in 

 the adult; in the third (cats) in both fetal and adult life; and in the 

 fourth (sheep, pigs, dogs, man, and others) in neither. 



Bouin and Ancel ('10) advanced a most plausible hypothesis, to the 

 effect that the interstitial cells are almost, if not completely, absent in 

 mammals which exhibit spontaneous ovulation (man, primates, dogs, 

 etc.), while, on the other hand, they are tremendously developed in mam- 

 mals of non-spontaneous ovulation (rabbits, guinea pigs, mice, rats, cats). 

 According to this view, the unusual development of the corpus luteum 

 compensates for the absence of the interstitial cells in the first group ; in 

 other words, a balance is maintained between the interstitial cells and the 

 periodic corpus luteum, which are, therefore, to be considered as strictly 

 homologous organs, producing the same internal secretion. Unfortunately 

 subsequent researches have failed to confirm the details of Bouin and 

 Ancel's classification of mammals into the two groups, so that we remain 

 absolutely in the dark. An interesting critique is given by Athias (e) ('10, 

 p. 185). 



Structure 



In the human ovary the interstitial cells are arranged without apparent 

 order, except that they show a tendency to be distributed in small clumps, 

 as is illustrated in Fig. 1. They are quite large and are roughly spherical 

 in shape. Sometimes they contain two or more nuclei, but this is the 

 exception, rather than the rule. Indications of the occurrence of amitotic 

 division are not uncommon. Mitoses are, of course, more numerous in 

 young animals. The nuclei are usually large, spherical and generally 

 poor in chromatin, at any rate in the human species. Regaud and Policard 

 ('01) were apparently the first to remark upon the peculiar polychro- 

 maticity of the nuclei in their studies on the rabbit and guinea pig. In 

 another study Dubreuil ( 7 Q6) claims that it is occasioned by the presence 

 of a diffuse, homogeneous substance in the nuclear sap. Athias ('10, p. 

 165) has found similar appearances in bats, and adds the observation that 

 the darkly staining nuclei are more abundant in old animals. Quite fre- 

 quently well formed nucleoli may be distinguished. Centrosomes occur 

 in the bat, but I have been able to discover no reference to their existence 

 in man. 



The cytoplasm has been carefully studied by many workers. It is 

 crowded with droplets of lipoid, which are dissolved out in routine prep- 

 arations, giving it a honeycomb appearance. The chemical composition of 

 this lipoid has not been definitely determined. Like the lipoids of the 



