GILSOjST : GENITALIA OF jSTEKXTINA FLUVIATILIS. 83 



is flask-shaped and divided into two parts by an annular constriction, 

 is the spermatheca. The fundus of the spermatheca is rehated to 

 a narrow canal (d.e.), which is really the upper part of the copulatory 

 branch of the oviduct. This canal increases in calibre as it approaches 

 the main oviduct, and opens into the glandular portion of that structure. 

 It may accordingly receive the name of comtectuuj duct. An irregular 

 cavity {d.f.) is formed at the meeting-point of this connecting duct 

 with the main oviduct, which I pi'opose to term the fertilization 

 or impregnation chaviher. 



Tlie terminology which I have employed is justified by a knowledge 

 of tlie process of fertilization, which takes place as follows : — The 

 spermatic fluid is deposited by the male in the bottom of the " vagina " 

 (h.c), and enters the copulatory vesicle i^v.c). This latter is then 

 found to contain numberless spermatozoa, no particular arrangement 

 being noticeable in their disposition. A short time after copulation, 

 the vesicle contracts, and the spermatozoa are pressed out and sent 

 down towards the vagina. They do not stay long in this, however, 

 but travel up into the flask-like spermatheca {sp.). AVithin that they 

 assume a radiate disposition, becoming arranged with extraordinary 

 regularity in a layer coating the inner wall of the vesicle, all heads 

 being turned towards the axis, the tails being directed outwards. 

 Towards the time of impregnation the spermatheca contracts also, 

 and the spermatozoa are sent out, not down to tlie vagina again, but 

 up into the cormecting duct {d.c ), in which they are to be found in 

 disorder. They thus reach the impregnation chamber (d.f.), which 

 the eggs, coming down through the oviduct, enter sooner or later. 

 Impregnation takes place, and the eggs are passed down into the 

 glandular portion of the incubatory branch {d.g.). They receive 

 there, first an albuminous coating, then the substance which makes 

 up the shell, and are finally extruded. 



It follows from this that the part Claparede designated the " uterus " 

 ("Gebarmutter," Fig. I,/) cannot be so termed, since it never receives 

 any egg. If the word "uterus " is to be used at all, it must be applied 

 to the glandular part of the oviduct (Fig. II, d.g.). The organ which 

 the Swiss naturalist considered as an accessory gland appended to the 

 oviduct (Fig. I, a) is, in fact, the lower section of the main genital 

 duct, the opening of which he had failed to discover. The really 

 accessory part of the system is that which he considered as the main 

 one, i.e. the copulatory chamber, with a special opening which 

 Claparede believed to be the only genital aperture. The connecting 

 duct he regarded as a narrow portion of the only genital duct he 

 believed to exist, whilst it is, in fact, only a communication between 

 the main (incubatory) and the accessory (copulatory) branches of the 

 forked oviducal system. These facts must needs be taken into account 

 by those who would undertake a comparative study of the genital 

 organs in Gastropoda ; and further details, together with a histological 

 description, will be forthcoming in a monograph of Neritina fluviatilis 

 which my assistant. Dr. Lenssen, has in course of preparation. 



