XIII] HELIX 295 



The only organs of the snail which remain to be mentioned are 

 the reproductive organs. These are exceedingly complicated in this 

 Mollusc, both sexes being united in the same individual, a condition of 

 affairs which is known as hermaphroditism. The essential genital 

 organ is the ovotestis, a small yellowish patch of delicate tubes 

 spread out on the surface of the liver, on the inner side of the 

 uppermost coil of the spire (Fig. 131). This organ produces both 

 eggs and spermatozoa and both travel down a single tube. Before 

 the duct reaches the neck it receives the secretion of a large organ, 

 called the albumen gland. This secretion consists of a fluid 

 which has proteids in solution and is of high nourishing value. 

 Beyond the albumen gland although externally simple the duct is 

 divided by a septum into two passages, one for the eggs and one for 

 the spermatozoa, and still further on it becomes completely divided 

 into two separate tubes. The female portion opens to the exterior 

 by a thick- walled muscular part, the vagina, into which a tuft of 

 tubes the mucous glands opens. The vagina also receives the 

 opening of an organ called the sperniatheca, which is a round 

 sac at the end of a long duct in which the spermatozoa received 

 from another individual are stored up. In addition to this, a 

 thick-walled sac called the dart- sac also communicates with the 

 vagina. In this sac is found a calcareous rod which is thrown out 

 into the body of another individual about the time of fertilisation. 

 The male duct also opens into a muscular organ called the penis, 

 which can be partly everted, that is, turned inside out, and so 

 protruded. The function of this organ is to transfer the sperma- 

 tozoa to another individual; it has a blind pouch projecting 

 inward beyond the place where the male duct enters it called 

 the f 1 age Hum : in this the spermatozoa are massed together into 

 bundles called spermatophores. Both penis and vagina have 

 a common genital opening far forward on the right side of the neck 

 (Fig. 127). 



Few Mollusca have such complicated generative organs as the 

 snail. One large group of marine snails, the Opisthobranchiata, 

 resemble Helios in being hermaphrodite, but none possess the dart- 

 sac, and in many the generative opening is placed further back and 

 connected with the opening of the penis by a groove called the 

 seminal groove. Hence the penis is obviously derived from a 

 muscular pit on the side of the head into which the spermatozoa 

 trickled and was at first unconnected with the generative opening. 



In another group of marine snails, the Prosobranchiata, there is 



