30 MOLLUSC A. 



MOLLUSCA. 



Lamellibranchiata. 



(21) H. Lacaze-Duthiers. "Organes geuitaux des Ace"phales Lamellibranches." 

 Ann. Sci. Nat., 4 me serie, Vol. n. 1854. 



(22) W. Flemming. "Ueb. d. er. Entwick. am Ei d. Teicbmuscbel. " Archiv f. 

 mikr. Anat., Vol. x. 1874. 



(23) W. Flemming. "Studieu iib. d. Eutwick. d. Najaden." Sits. d. k. Akad. 

 Wins. Wien, Vol. LXXI. 1875. 



(24) Th. von Hessling. "Einige Bemerkungen, etc." Zeit. f. u-iss. Zool., 

 Bd. v. 1854. 



(25) H. von Jhering. "Zur Kenntniss d. Eibildung bei d. Muscbeln." Zeit. f. 

 wiss. 'Zool., Vol. xxix. 1877. 



(26) Keber. De Introitu Spermatozoorum in ovula, eie. K ; ^nigsberg, 1853. 



(27) Fr. Leydig. " Kleinere Mittheiluug etc." Mailer's Archiv, 1854. 



Gasteropoda. 



(28) C. Semper. "Beitrage z. Anat. u. Physiol. d. Piilmonaten. " Zeit. f. wiss. 

 Zool., Vol. vin. 1857. 



(29) H. Eisig. "Beitrage z. Anat. u. Entwick. d. Pulmonaten." Zeit. f. wiss. 

 Zool., Vol. xix. 1869. 



(30) Fr. Leydig. "Ueb. Paludina vivipara. " Zeit. f. iviss. Zool., Vol. n. 1850. 



Cephalopoda. 



(31) Al. Kolliker. Entwic.klungsgeschichte d. Cephalopoden. Zurich, 1844. 



(32) E. II. Laukester. "On the developmental History of the Mollusca." Phil. 

 Trails., 1875. 



Lamellibranchiata. 



The ova of the Lamellibranchiata present several points of 

 interest. They are developed in pouches of the ovary which are 

 lined by a flattened germinal epithelium, or sometimes (?) a syncy- 

 tium. Some of the cells of this epithelium enlarge and become 

 ova, but remain attached to the walls of their pouches by proto- 

 plasmic stalks. Round the ovum there appears in some forms 

 (Auodoii, Uuio) a delicate vitelline membrane, which is incomplete 

 at the protoplasmic stalk, and is therefore perforated by an aperture 

 which forms the micropyle. (Fig. 12.) As the ovum becomes ripe 

 a large space filled with albuminous fluid becomes established 

 between the ovum and its membrane, but the ovum remains attached 

 to the membrane at the micropyle. In Scrobicularia (von Jhering 

 No. 25) the membrane round the ovum appears from the first as an 

 albuminous layer, the outermost stratum of which becomes subse- 

 quently hardened as the vitelline membrane. In this form also the 

 protoplasmic stalk becomes, in pouches largely filled with ova, 

 extremely long. The ova become eventually detached by the stalk 

 rupturing, and the portion of it which remains attached to the vitel- 

 line membrane falling off. The function of the stalk and of the 

 micropyle during the development of the ovum is undoubtedly a 

 nutritive one. 



