V PERIODICITY IN BREEDING I 29 



the method in certain species of Limax deserves special notice. 

 L. maximus has been observed at midnight to ascend a wall or 

 some perpendicular surface. A pair then crawl round and round 

 one another emitting a quantity of mucus which at length forms 

 a patch, 2 to 2^ inches in diameter. When this acquires con- 

 sistency the pair begin to twist round each other in corkscrew 

 form, and detach themselves from the wall, hanging by a cord 

 of the thickened mucus, about 8—15 inches long, and still twist- 

 ing round each other. The external generative organs are then 

 protruded and copulation takes place, after which the bodies 

 untwist, separate, and crawl up the cord again to the wall.^ 



Periodicity in Breeding, — In the marine MoUusca, the 

 winter months appear to be the visual time for the deposition of 

 eggs. Careful observations have been made on the Mollusca 

 occurring at Naples,- and the general result seems to be that for 

 all Orders alike the six winter months from November to April, 

 roughly speaking, are the breeding time. Scarcely any forms 

 appear to breed habitually in August, September, or October. 

 On our own coasts, Nudibranchiata come in shore to deposit 

 their ova from January to April. Furpura lapilliis may be 

 observed depositing ova all the year round, but is most active 

 from January to April. Biiccinuin undatum breeds from October 

 to May ; Littorina all the year round. 



The land Mollusca exhibit rather more periodicity than the 

 marine. In temperate climates they breed exclusively in the 

 summer months. In the tropics their periods are determined 

 by the dry and rainy seasons, where such occur, otherwise they 

 cohabit all the year round. According to Karl Semper, the 

 snails of the warm Mediterranean region arrive at sexual maturity 

 when they are six months old, i.e. before they are fully grown. 

 After a rest of about three months during the heat of summer, a 

 second period of ovipositing occurs.^ Helix hortensis and H. 

 nemoralis ascend trees, sometimes to a height of forty feet, when 

 pairing.* 



Hybridism as the result of union between different species of 

 Mollusca is exceedingly rare. Lecoq once noticed ^ on a wall at 

 Anduze (Gard) as many as twenty specimens of Pupa cinerea 



1 J. Bladon, Zoologist, xvi. p. 6272. 



2 Lo Bianco, MT. Zool. Stat. Neap. viii. p. 414. ^ Animal Life, pp. 126, 135. 



■* R. Rimmcr, Land and Fresh- JFater Shells, p. 119. ^ Joum. de Conch, ii. p. 245. 

 VOL. Ill ^ 



