OVIPOSITION AND CHARACTEP. OF THK EGG-CAPSULES AND EGG. 101 



Sub-order 2. Gytunosomata. Without shell and mantle. 

 Olione., Pneumodermon. 



IV. PULMONATA. 



Principally fresh-water or terrestrial. Ctenidium wanting ; 

 mantle-cavity modified as a lung. The pleurovisceral 

 commissures are not crossed. Hermaphrodite. 

 Sub-order 1. — Onchidiacea. Marine or littoral, without 

 shell ; anal and pulmonary orifice posterior. 



Onchidium, Vaginulus. 



Sub-order 2. — Basommatophora. Fresh-water and terres- 

 trial (usually maritime) Pulmonates. Eyes at the bases 

 of the tentacles. 



Limnaea, Planorbis, Ancylus, Aurictda. 



Sub-order 3. — Stylommatophora. Terrestrial Pulmonates. 



Eyes at the tips of the tentacles. 



Succinea, Vitrina, Claimlia, Bulimus, Helix, Test art'/ hi, 

 Daudebardm, Limaz, Arhn. 



1. Oviposition and Character of the Egg-capsules and Egg. 



The Gastropoda * are mostly oviparous, but oviposition takes place 

 in such a variety of ways that we can only give a few examples. 



An exceedingly simple method of oviposition is found in Patella, 

 the eggs of which are laid singly and are apparently fertilised in the 

 water, as copulatory organs are wanting in this genus. It was there- 

 fore possible to fertilise these eggs artificially (Patten, No. 82). 

 Each egg is surrounded by a somewhat thick radially striated en- 

 velope which has a funnel-like projection with a wide aperture (the 

 micropyle). 



In most Gastropoda, however, fertilisation takes place within the 

 body of the mother, and the eggs are not laid singly but unite to 

 form larger or smaller masses of spawn. The spawn may have the 

 form of disc-shaped or long hyaline gelatinous masses (fresh- water 

 Pulmonates). Each egg within the gelatinous mass is further 



* A more detailed description of the spawn of land and fresh-water Gastro- 

 pods is given by Pfkiffkh (No. 88). A detailed account of oviposition in 

 Gastropods and notices of the literature on the subject are given by KEFEB- 

 . i No. 52) and can also be obtained from the treatises referred to in the 

 Literature. [A good general account of the egg-capsules will be found in 

 Fischer's Manuel ch C"/u7/////<>/<></(>, 1S87. — Ed.] 



