102 RAYMOND PEARL AND WILLIAM FREEMAN SCHOPPE 



In dealing, in this and the earlier work referred to, with oocytes 

 visible to the unaided eye alone, the tacit assumption is that the 

 number of such visible ova is correlated to a high degree with 

 the undetermined — and indeed undeterminable — total number of 

 ova in the ovary. Tlie work of von Hanseman^ and of Kappeli' 

 indicates that this assumption is justified. Occasionally a case 

 turns up, as will be shown presently in detail, where the physical 

 condition of the bird's ovary as a whole greatly raises the limit 

 of oocyte visibility, so to speak. This condition, however, we 

 have found to occur but once in nearly forty birds examined from 

 this point of view. So far as concerns the remainder of the 

 counts, we are convinced, after direct experience with the material, 

 that the ratio between visible ova and mass of the ovary as a 

 whole, and by inference the number of invisible ova, is normally 

 a rather constant one, and that consequently our material is as 

 homogeneous and trustworthy as any statistical data on the soft 

 parts of animals. 



Regarding the method of counting, the following may be 

 added to what was said in the earlier paper (loc. cit., p. 296), 



The ovaries, when taken from the birds, were placed in a 10 

 per cent solution of formalin, in order to preserve them until 

 counts could be made. In making the earlier counts, fresh 

 ovaries were at first used, but later after trying various preser- 

 vatives it was concluded that the use of formalin was most satis- 

 factory, as it preserved the ovaries in perfect condition and made 

 counting possible at any time. 



The functioning ovary when taken from the bird closely 

 resembles a bunch of grapes. It is made up of a large number of 

 oocytes held together by connective tissue, joined to a heavy 

 stalk by which they are held in place in the body. 



The oocytes are of various sizes, and for convenience in count- 

 ing four divisions were made : a) follicles from which the ova have 

 been discharged; b) oocytes over 1 cm. in diameter; c) those over 

 1 mm. and less than 1 cm.; d) those less than 1 mm. 



^liansemann, D. Ueber den Kampf dcr Eier in den Ovaricn. Arch. f. Ent- 

 wicklungsmech., 1912, Bd. 35, S. 223-235, 1 pi. 



^Kai)peli, I. Bcitragc zur Anatomic und Physiologic dcr Ovaricn von wild- 

 lebenden und gczilhmten Wiederkiiucrn und Schwcincn. Bern, 1908, K. J. 

 Wyss. 78 pp., 5 tab., 6 pi. 



