ORGANS OF GENERATION. 



411 



being easily distinguished in rapid action 

 through the pellucid coverings of the egg. 



In the Cirrhopoda we have most probably 

 an example of this mode of generation, pre- 

 suming, that is, that the opinions of Cuvier 

 upon this subject are correct. These opinions, 

 it is true, have been disputed by various 

 authorities, as will be evident on reference 

 to the article CIRRHOPODA ; but their correct- 

 ness has been so fully supported by the 

 dissections of John Hunter, recently given 

 to the world,* that it seems best at least to 

 pause before repudiating the conclusions to 

 which these great anatomists, unacquainted 

 with the labours of each other, were indivi- 

 dually conducted. In the Cirripeds the ovaria 

 are two in number, placed on each side of 

 the stomach ; the two oviducts which proceed 

 from these unite to form a single elongated 

 tube, the parietes of which are thick and 

 apparently glandular. It is evident that in this 

 case the walls of the common canal, or ovipo- 

 sitor as it is usually termed, may serve to 

 secrete a seminal fluid, impregnating the eggs 

 at the period of their extrusion ; and such, 

 in the opinion of the authors above mentioned, 

 is a part of its office. 



THIRD DIVISION. Ovigerous and impreg- 

 nating organs co-existent, but the co- 

 operation of two individuals necessary 

 for mutual impregnation. 



This arrangement of the generative system 

 occurs in some of the Parenchymatous Entozoa, 

 in the Annelida, and also in the Pteropod and 

 some Gasteropod Mollusca. Some of the 

 Entozoa, as Fasciola and Planaria, furnish 

 the simplest examples of this hermaphrodite 

 condition. In these creatures the male organs 

 consist of spermatic cceca, communicating with 

 a minute extensible penis, which is placed 

 behind the oral sucker. Near the penis a 

 small orifice is seen, leading to the ovigerous 

 canals, which have no communication with 

 the impregnating apparatus ; and the copula- 

 tion of two individuals is thus indispensable 

 to a reciprocal fertilization of the ova. 



Those of the Annelida in which the gene- 

 rative system is best understood are androgy- 

 nous, and mutually impregnate each other, 

 although it is probable that in the tubicolous 

 genera, which are immoveably fixed to the 

 same spot, and almost deprived of locomotion, 

 each individual may in itself be sufficient for 

 reproduction. 



In the Abranchiate and Dorsibranchiate 

 Annelida the male apparatus is composed of 

 several pairs of secreting bodies, arranged on 

 each side of the mesial plane, those of the 

 same side communicating with each other by 

 a common vas deferens. In the Leech the 

 vasa deferentia, which convey the secretion of 

 the numerous testicular masses, terminate in 

 a long protractile tubular penis, and at a short 

 distance behind this the opening which leads 



* Catalogue of the Physiological Series of Com- 

 parative Anatomy contained in the Hunterian 

 Collection, vol. i. 



to the female parts may be discovered. These 

 latter consist of a simple uterine sacculus, or 

 receptacle for the ova, to which two minute 

 ovaries are appended. The congress of two 

 individuals is effected by the reciprocal in- 

 troduction of the organs of intromission into 

 the vulvse. In the Earthworm and Nais the 

 intromittent apparatus is deficient, so that 

 some authors have even doubted that the 

 process of copulation, which is undeniably 

 essential to fecundity, does more than stimulate 

 each individual to self-impregnation. In the 

 Earth-worm, as well as in Arenicola and 

 Aphrodita, the ova, after escaping from the 

 ovaria, are retained in the cellular meshes 

 which surround the alimentary canal, in which 

 they are not unfrequently hatched, the young 

 being most probably expelled through a tubular 

 aperture at the posterior extremity of the body. 

 As regards the generative system, the Pte- 

 ropod Mollusca approximate the more complex 

 type seen in the Gasteropoda. In Clio lorealis, 

 the ovary, which is partially enveloped by the 

 liver, gives off a slender duct, which, after 

 a short course, plunges into a glandular tube ; 

 this, becoming gradually narrower, terminates 

 in a round sac placed on the left side of the 

 head, where it opens externally : near this 

 point is the penis, or organ of intromission, 

 communicating with a small sacculus, by 

 which the male secretion is probably furnished. 



Fig. 200. 



Testia of Helix. 



The most complicated forms of this species 

 of hermaphrodism are met with in the Gas- 

 teropod division of Mollusca, existing through- 

 out the Nudibranchiate, Tectibranchiate, In- 

 ferobranchiate, and Heteropod orders, as well 

 as in those pulmonary genera which are un- 

 provided with a calcareous operculum. In 

 all these cases the testis is single and divided 

 into lobuli, connected together by the divisions 

 of the vas deferens so as to exhibit a racemose 

 arrangement, and each lobule, on minute in- 

 spection, is found to consist of little peduncu- 

 lated vesicles (Jig. 200). A slender vas defe- 

 rens conducts the secretion of this testicle to 

 the base of an intromittent organ of a most sin- 

 gular description ; this is a muscular tube of 

 great length, which, when not in use, is in- 

 verted and concealed within the body, but ca- 

 pable of protrusion at the will of the animal. 

 The female portion of this system is composed 

 of one ovary, provided with an ample and 

 tortuous oviduct, which serves, indeed, as a 

 kind of uterus or egg receptacle, wherein the 

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