I20 THE PHYSIOLOGY OF REPRODUCTION 



cells have a connective tissue origin, but these investigators do not 

 appear to have traced the successive stages of cellular developmejit 

 with the same completeness as Miss Lane-Claypon.^ Sainniont is of 

 opinion that they have a trophic function, a suggestion which was 

 first made by Pihiger.^ 



There would seem to be no doubt that the developing ova in the 

 immature ovary subsist and grow at the expense of the surrounding 

 tissue. Thus protoplasmic masses, formed by the aggregation of 

 very young ova, have been described by Balfour,^ who made the 

 suggestion that one ovum may develop at the cost of the others. 

 These aggregations of ova were noticed in the ovary of the fcBtal 

 rabbit at about the sixteenth day of pregnancy. A day or two 

 previously the ova were observed to be separate. Miss Lang-Claypon, 

 who confirms the observation, is of opinion thaj; Balfour's suggestion 

 was right, and that the ova which disappear serve ultimately as 

 food-stuff for the one ovum whose condition happens to be the most 

 vigorous. " This cannibalism on the part of J;he young ovum is not 

 surprising, if the life of an ovum be considered. It is really but the 

 normal condition of the cell at all its stages of development ; it grows 

 and fattens at the expense of other cells. In the young ovary, it is 

 starting its first stage of growth and must devour other cells ; later 

 on, during the growth of the follicle, it lives upon the follicle-cells, 

 and later still, when, after fertilisation, the [term] ovum in its 

 extended sense refers to the young foetus, [this latter] lives on the 

 material provided by the cells of the maternal organism." * 



Maturation and Ovulation 



The youngest and smallest Graafian follicles lie near the surface 

 of the ovary, but pass inwards as they increase in size. The large, . 

 mature follicles, however, ^come to lie just below the surface from 

 which they begin to protrude visibly at the approach of the breeding 

 season. During the prooestrum one or more follicles (the number 

 varying in different animals, according to the size of the litter) may 



' According tp Popoff {Arch, de Biol., vol. xxvi., 1911) tte origin of the 

 interstitial cells may vary with the species (mole, stoat, dog). For description 

 of interstitial cells in the guinea-pig see Atkins (Anat. Am., vol. xxxix., 1911), 

 and in man see Wolz {Arch. f. Oynak., vol. xcvii., 1912), and see above, p. 114. 

 See also Schaetfer {Arch.f. Oynak., vol. xciv., 1911). 



^ Pfliiger, Ueber die Eierstoche der Sdiigethiere und des Alenschen, Leipzig, 

 1863. 



' Balfour, loc. cit. 



* Lane-Olaypon, "On Ovogenesis, etc.," loc. cii. That one ovum may de- 

 velop at the expense of others is particularly well shown in Hydra, Tubularia, 

 and certain other Coelenterates. The nuclei of the ingested ova continue to 

 be easily recognisable even during the early segmentation stages of the 

 developing egg. 



