BITHINIA. 13 



This excellent genus was very properly separated from 

 Paludina by Mr. Gray. Unlike the Mollusks of the last 

 group, the Bithiniee are oviparous. M. Bouchard-Chan- 

 tereaux has given an interesting account of their pro- 

 ceedings when lajang their eggs ; as this is probably 

 not accessible to most of our readers, we quote it with 

 slight abridgment. The Bithinia tentaculata lays from 

 May to August. There are usually from thirty to seventy 

 globular, yellowish, hyaline eggs, which are united to- 

 gether in a band, and attached to stones or the stems 

 of aquatic plants. When the animal desires to lay, it 

 seeks some smooth place, and begins to clean the surface 

 with its mouth before commencing. That being done, 

 it contracts its foot so as to render itself a third shorter 

 than its usual dimensions when creeping, but also a third 

 broader. Then, ceasing to use its mouth, it raises the 

 centre of the anterior extremity of its foot, so as to form 

 a little canal, intended to receive the e^g. It next with- 

 draws its head a little within the shell, and directs its 

 muzzle towards the branchial orifice, where an egg appears 

 which it seizes and guides into the little canal to fix it 

 in its destined locality. Then the animal cleans the body 

 to which it adheres anew, and deposits a second egg, 

 repeating the operation until at last all the eggs are 

 expelled, and arranged in riband-fashion, each band, when 

 laid by an adult, consisting of three rows. The whole 

 process proceeds slowly, time being left between each 

 effort sufficient for the agglutination of the egg. The 

 young ones emerge at the end of from twenty to twenty- 

 five days, and do not attain full growth until the end 

 of their second year. 



