Messrs. Hancock and Bmhleton on the Anatomy of Eolis. 95 



introduction of the elongated, conical and pointed penis, fig. 5 a, 

 into the small simple channel of the spermatheca, tig. 2 i', along 

 which we believe it to pass to at least beyond its junction with 

 the oviduct, if not quite to the spermatheca itself. The penis, as 

 represented in the Plate, is from a specimen preserved in spirits, 

 but in the living state this organ is capable of taking a much 

 more elongated and attenuated form. 



The way in which fecundation is effected will be understood if 

 we now trace the passage of the ova from the ovary to the external 

 orifice : they pass along the oviduct, fig. 2 e, and are detained 

 awhile in the dilated and convoluted part of it, /, probably to re- 

 ceive some necessary investment ; after this they are conducted 

 forwards to where the testis joins the oviduct at k; here they are 

 subjected first of all to the influence of the seminal fluid of the 

 individual itself, for there appears to be little or no doubt that 

 the double muscular coating of the testis, c, is capable of driving 

 its contents either outwardly towards the penis a, or if required, 

 inwardly towards the oviduct e' '. Ciliary motion may also assist 

 in determining the flow of the seminal fluid in either direction. 

 The operation of this self-fecundation being thus accomplished 

 in the first instance, the ova are secondly conveyed backwards to 

 the duct of the spermatheca at /, where they undergo the action 

 of the semen injected into that receptacle from another animal 

 during the sexual union ; afterwards they are carried into the 

 right duct of the mucus-gland at n, which is freely continuous 

 with the left duct, and with the common female channel of out- 

 let b. 



In the wide ducts of the mucus-gland the ova receive their last 

 coating and their peculiar arrangement in it, and lastly they are 

 expelled through the female orifice b' , the form of the channel 

 probably impressing upon the continuous strap or cord of mucus- 

 enveloped ova the peculiar form which the spawn of the different 

 species is found to possess. 



It will thus be seen that a double impregnation is here pos- 

 sible, and indeed more than probable, considering the anatomical 

 relation of the parts ; but whether it be in every instance essen- 

 tial, we are not prepared to state. If the experiments of M. Alex, 

 de Nordmann related in the c Annales des Sciences Naturelles/ 

 3 me serie, tome v. 1846, touching the breeding of Tergipes, which 

 we consider a member of the genus Eolis, be thought conclusive, 

 it may be deemed that self-impregnation is alone requisite. Since 

 however copulation is observed to take place among these ani- 

 mals frequently and freely, even in confinement in the house, we 

 have little doubt of the necessity of a double impregnation. 



On a review of our description of the generative organs in the 

 above-mentioned species of Eolis, it appears that these organs 



