THE OVUM. 



1C 



ft 



character similar to that 

 of the goblet-cells of a 

 mucous membrane, and 

 pour out their metamor- 

 phosed protoplasm into 

 the body of the ovum. 



After the above mode 

 of nutrition has gone on 

 for a certain time a 

 change takes place, and 

 the ridges gradually dis- 

 appear. This is caused 

 by the epithelial cells 

 passing off from the 

 ridges into the proto- 

 plasm of the ovum ; and 

 becoming assimilated, 

 after retaining their in- 

 dividuality for a longer 

 or shorter period. When 

 the absorption of the 



ridges is completed the surface of the ovum assumes a perfectly 

 regular outline. The capsule of the ovum then bursts at the 

 opposite pole to the peduncle, and the ovum falls into the 

 oviduct. 



The ova of the Cephalopoda, like those of the Gasteropoda, 

 are quite naked, being without a vitelline membrane or chorion. 

 The egg-capsule which is formed for them in their passage down 

 the oviduct is perforated in Sepia by a micropylar aperture. 



FIG. 14. TRANSVERSE SECTION THROUGH AN 

 OVARIAN EGG OF SEPIA. (Copied from Lankester.) 



o.c. outer capsular membrane, i.e. inner cap- 

 sular membrane with follicular epithelium, b.v. 

 blood-vessels in section between the outer and 

 inner capsular membranes, c. vitellus. 



The section shews the folds of the inner 

 capsule with their epithelium, which penetrate 

 into the substance of the ovum for the purpose 

 of supplying it with nourishment. 



CH^ETOPODA. 



(33) Ed. Claparede. " Les Annelides Chaetopodes d. Golfe de Naples." 

 Mem. d. I. Societ. phys. ct d'hist. nat. de Geneve 1868 9 and 1870. 



(34) E. Ehlers. Die Borstemviirmer nach system, itnd anat. Untcrsuchnngcn. 

 Leipzig, 1864 68. 



(35) E. Selenka. "Das Gefass-System d. Aphrodite aculeata." Nieder- 

 linidisches Archiv f. Zoo!., Vol. n. 1873. 



The ova of the Chaetopoda are in most cases developed from 

 the special tracts of the epithelial cells lining parts of the body 



