THE OVUM. 



33 



character similar to that of 

 the goblet-cells of a mucous 

 membrane, and pour out 

 their metamorphosed proto- 

 plasm 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 disappear. This 

 is caused by the epithelial 

 cells passing off from the 

 ridges into the protoplasm 

 of the ovum; and becoming 

 assimilated, after retaining 

 their individuality for a 

 longer or shorter period. 

 When the absorption of the 

 ridges is completed the sur- 

 face of the ovum assumes 

 a perfectly regular outline. 

 The capsule of the ovum 

 then bursts at the opposite 



FIG. 14. TBANSVEBSE SECTION THROUGH AN 

 OVAEIAN EGG OF SEPIA. (Copied from Lankester.) 



o.c. outer capsular membrane, i.c 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. 



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. 



CH^ETOPODA. 



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

 ?. Societ. phys. et d'hist. nat. de Geneve 1868 9 and 1870. 



(34) E. Ehlers. Die Borstenwurmer nach system, und anat. Untersuchungen. 

 Leipzig, 186468. 



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

 Archivf. Zool., Vol. n. 1873. 



The ova of the Chsetopoda are in most cases developed from the 

 special tracts of the epithelial cells lining parts of the body cavity, which 



FIG. 15. A PABAPODIUM or TOMOPTERIS. (From Gegenbaur.) 

 o. Collection of germinal epithelial cells lining the body cavity. 



B. E. 



