OVUM. 



[107J 



Fig.ll 



Genital Organs of Phyllirhoe bucephalum, one of the Hermaphrodite Gasteropoda. (From H. Mutter and 



Gegenbaur.) 



A. The compound or hermaphrodite organs dissected out and represented several times magnified ; 

 o t, the two productive organs each composed of ovigerous and seminiferous parts ; v d, the common 

 excretory ducts for both kinds of organ ; v s, the seminal vesicle ; u, the uterus ; p, a part of the 

 penis ; c, the common external vent. 



B. One of the lobes of the common productive organ laid open and more highly magnified. 

 Towards the surface o o, the ova are seen in different stages of development in the ovarian stroma ; in 

 the interior t t, the substance of the testis with spermatic cells and spermatozoa in various degrees 

 of advancement ; some of the filaments being very long ; v d, the common excretory duct for ova and 

 spermatozoa. 



enclosed in the liver, the nature of which was 

 for along time involved in obscurity, and occa- 

 sioned much doubt and difficulty to naturalists. 

 The explanation of this peculiar structure we 

 owe first to H. Meckel*, and Leuckartf ; and 

 more recently H. Meckel and Gegenbaur have 

 described this organ particularly in one of the 

 heteropodous Mollusca,viz. Phyllirrhoe buce- 

 phalum.J The outer part of this curious organ 

 constitutes the ovary, the inner the testis ; and 

 the products of these respective organs, in 

 leaving the seat of their first formation, pass 

 together into an inner common cavity, and 

 thence downwards in the excretory duct. 

 There is, therefore, a common outlet for both. 

 The ova and spermatozoa most frequently 

 pass out at different times ; but occasionally 

 both these reproductive elements are seen to- 

 gether in the passages. It seems probable 

 therefore that they in general meet for im- 

 pregnation only in the lower part of the pas- 

 sages ; but this apparently is not yet fully de- 

 termined, and the modes of union may be 



* Miiller's Archiv. for 1844, p. 483., see plates 

 xiv. and xv. 



f Zur Morphologic und Anatomic der Geschlechts 

 Organ. 1847, p. 128. 



J Zeitsch. fur VVissen. Zool. vol. v. p. 355. pi. xix. 



various in different genera or families. At 

 all events, the primitive ova and spermatozoa 

 seem to come into contact with each other 

 previous to the addition of the enveloping 

 membrane. * 



The ova of the Mollusca are in general of 

 small size. The yolk consists of a viscid al- 

 buminous substance, containing suspended in 

 it minute granules, and a variable quantity of 

 coloured oil globules. The germinal vesicle 

 is proportionally of considerable size ; and the 

 macula is distinct and granular. Leuckart -j- 

 states that he and Nordmann have ascertained 

 that in Lymneus, the first part of the ovum 

 which is formed is the germinal vesicle, that 

 the yolk-substance begins as a clear trans- 

 parent albuminous matter surrounding the 

 germinal vesicle, and, as we have seen in various 

 other animals, the granular yolk matter is 

 gradually deposited in this clearer part of the 

 vitelline substance, occupying at first princi- 



* The hermaphrodite gland exists in the Ptero- 

 poda, Apneusta, Nudibranchia, Infero-branchia, Tec- 

 tibranchia, and Pulmonata. The Mollusca which 

 have separate sexual organs belong chiefly to the 

 orders Cyclobranchia, Scutibranchia.Tubulibranchia, 

 andCirribranchia, some Heteropocla, Pectinibranchia, 

 and operculate Pulmonata or Cyclostoma. 



t Article Zeugung, p. 800. 



