SEXUAL ORGANS. 123 



vidual plajdng the part of male and female at the same time ; 

 the genital vestibule is thrust out, the penis is unrolled like the 

 finger of a glove and introduced into the vagina. The sperm is 

 surrounded sometimes by an elongated filiform capsule, which 

 is dilated for its anterior third with crenulated edges, or salient 

 ridges, and which is called a spermatophore or capreolus. Such 

 spermatophores are found in Arion, Parmacella, Peltella, 

 Hyalina, Bulimulus, and in a large number of Helices, but in 

 some of the latter genus they do not exist. 



The presence of a spermatophore in the verge of each indi- 

 vidual during copulation, evidently proves that fecundation 

 must be reciprocal ; nevertheless the pulmonates may copulate 

 several times, as Yan Beneden has found two spermatophores 

 in the copulatory pouch of a Parmacella, and Fischer has seen 

 four in that of Bulimulus Delattrei. 



I have watched the copulatorj'^ act in American Helices, con- 

 fined under a bell glass, and have been amused by the stupidity 

 with which two individuals , each similarly minded , would continue 

 to crawl arou.nd each other for many minutes, both so desirous 

 to play the active part that neither was willing to remain 

 immobile the moment necessary to secure the juxtaposition of 

 their organs. 



The spermatophore is formed in the deferent canal (Hyalina), 

 or in the verge or its flagellum (Helix) ; after its dissociation in 

 the copulatory pouch, the sperm is set at liberty ; the sperma- 

 tozoa enter the canal of this pouch and pass into the uterus ; 

 finally arriving in the epididymic csecum, where they fecundate 

 the ovules. 



Terrestrial mollusks lay but few eggs ; which are covered 

 usually by a soft skin, but in the Testacella and tropical species 

 of Bulimus and Achatina the egg is protected by a calcareous 

 shell. The group Borus, including the largest species of 

 Bulimus, inhabits the tropical regions of Brazil ; the eggs of 

 these shells are about an inch in length, or fully the size of a 

 pigeon's egg (xvii, 100), with a shell of about the same thickness. 

 The natives eat them. In a similarly isolated group of Achatina, 

 inhabiting tropical Africa the eggs are equally as large as Borus. 

 Generally the eggs are laid in a shallow hole dug in the ground 

 and covered over, but some of the arboreal Philippine Island 

 Bulimi construct a rude nest by curling up the leaf of a tree, in 

 which they oviposit. 



Fresh-water pulmonates, Limnaea, Physa, etc., lay from twenty 

 to one hundred eggs, Ancylus, five or six ; these are enveloped 

 together in a gelatinous material. 



The opisthobranchiates form a spirally rolled ribbon-like 

 capsule for their eggs ; such are those of Aplysia, Doris (xvii, 

 9T), Bullsea, Eolis. A somewhat similarly shaped capsule, 



