272 MR. F. E. BEDDARD ON THE [May 4, 



2. Observations on the Ovarian Ovum of Lepidosiren [Pro- 

 topterus). By Fbank E. Beddard, M.A., F.R.S.E., 

 Prosector to the Society. 



[Eeceived May 3, 1886.] 



(Plates XXVIII. & XXIX.) 



I. Introduction, p. 272. 

 II. Egg-membranes, p. 273. 



III. Germinal Vesicle, p. 276. 



IV. Follicular Epithelium and Development of Yolk, p. 279. 

 V. Postembryonic Origin of Ova, p. 288. 



VI. E6sum6, p. 291. 



I. Introduction. 



A recent memoir on the anatomy of the Dipnoi by Howard 

 Ayers ' contains some account of the ovaries and the ova in Lepido- 

 siren'^, ilhistrated by several figures. The description of these organs 

 is, however, mainly anatomical ; and though in the figures some 

 histological details of the ovary and the contained ova are to be 

 found, their structure is not described. The autlior contents 

 himself with remarking upon the similarity to the Amphibia, and 

 all that I can find in his paper about the minute structure of the 

 ovaries and ova is the following paragraph ^ : — " Die Structur der 

 Eierstocke ist direkt vergleichbar mit der der Urodelen. Die ver- 

 schiedenen Stadien in der Entwickelung der Eier aus dem Keimepithel 

 sind, soweit bei dem in Alcohol konservirten Material festgestellt 

 werden konnte, wesentlich dieselben, wie sie fiir niedere Wirbelthiere 

 constatirt sind. Wenn die Eier vollig entvvickelt sind, so ist eine 

 Ilalfte ihrer Oiierfliiche pigmentirt (diejenige, welche gegen die 

 freie Hiilfte des Eierstockes gerichtet ist), wjihrend die andere 

 Hiilfte farblos bleibt"^. Furthermore, in describing the anatomical 

 relations of the different parts of the genital system, Dr. Ayers 

 takes occasion to remark that the sexual cells (both ovaries and 

 testes) are inclosed in two delicate sacs — an outer peritoneal, and an 

 inner formed by the connective-tissue stroma. 



I shall refer more particularly to the appearances depicted in 

 Ayers's figures in considering the structure of the ovaries and ova 

 as I interpret them from my own preparations. 



^ "Beitrage zur Anatomie und Physiologie der Dipnoer," Jenaische Zeitsehr. 

 vol. xfiii. (188.5), pp. 479-527, 3 plates. 



^ The specimen studied by myself is from the Nile, and would therefore, 

 according to some authors, be moi-e properly termed Protoj^teriis. Dr. Ayers 

 shows reasons for assuming that there is really no generic distinction between 

 the American Lejndosiren and the African Protopterus ; the former name sliould 

 therefore, on grounds of priority, be retained. 



3 Loc.cit:p. 508. 



* This is a curious point of similarity to the ova of the Frog (see Balfour, 

 Comp. Embr. vol. ii. p. 99; Pfliiger, Arch. f. d. ges. Physiol. Bd. xxxi. 1883), 

 not remarked upon by Ayers in his paper. 



