OF THE WATER-SNAIL AND MUSSEL. 221 



On the Oviparous Water-snail [Limnea stagnalis\. 



This water-snail spawns its spawn enclosed in a fine jelly, perhaps 

 about fifty [eggs] at a time. The egg when taken out of the jelly is a 

 round body, a little flattened and a little oval ; it has a pretty strong 

 coat. When burst, a transparent jelly comes out: there is no yolk 1 . 

 In a few days after the spawning, the small shell is seen forming in this 

 little body like a white spot, which increases till it occupies the whole. 

 When those little spots, or snails, are only about the lOOdth part of the 

 size of the whole, we see them moving in the egg 2 . The question is, 

 how are they nourished ? Do they drink the contents ? have they any 

 connexion by way of absorption ? In about three weeks they begin to 

 hatch and come out of their shells. The slime in which the ova are 

 enclosed does not coagulate in. spirit. 



On the Viviparous Water-snail [Paludina vivipard]. 



In the middle of July they appear to be completely pregnant, the 

 uterus full of young in all their stages 3 , from the gelatinous ovum or 

 embryo to the complete snail, with its shell formed and capable of 

 moving about with ease. The number in one snail about fifty or sixty. 



Generation of the Mussel \Anodon cygneus] . 



In the beginning of July these appear very fleshy and [their soft 

 parts] fill the shell. The outer membrane [mantle] appears granulated, 

 and much like the ovarium of several fishes. This granulated appear- 

 ance is also seen on that fleshy mass [ovarium or testis, with the liver], 

 in which the intestine takes its turns. These [gramdations or ova] 

 !-eem in prodigious numbers ; and sometimes I have seen these ova 

 becoming of a darker colour, but not so as to be clear that they were 

 young mussels. 



The mussel, as well as most other animals, is subject to animals 

 living upon it. They seem like a beetle in shape, and are about the 

 size of a large pin's head, with a large body, long legs jointed, and 



1 [No ' food-yolk' appended to the 'germ -yolk.'] 



2 [The rotation of the germ-yolk and embryo on its axis is produced by the action 

 of vibratile cilia on the surrounding albumen. The development of the Limnea is 

 well described by Pfeiffer in his ' Naturgeschichte deutscher Land- und Siisswasser- 

 Mollusken,' 4to. 1825. See also my ' Lectures on Invertebrata,' 8to. 1855, p. 569. 

 Hunt. Prep. No. 2313.] 



3 [Hunt. Preps. Nos. 2942, 2943.] 



