94 GASTROPODA. 



in the Eolididcs. As an example of the number 

 deposited, I may mention that a specimen of Eolis 

 l)aj)illosa has this spring laid, in one of my tanks, 

 nine strings of spawn, between the 20th of March 

 and the 24th of May, all as nearly as possible of 

 the same length. Each string contains about 

 100 convolutions, each convolution about 200 ova, 

 and each ovum including on an average two 

 embryos, making a total progeny of 360,000, 

 produced from one parent in little more than two 

 months. 



The young, when hatched, have a minute trans- 

 parent nautilus-shaped shell, from which protrudes 

 a head furnished with a pair of large swimming- 

 fins, so that they may be compared with the 

 Pteeopoda. The fins are richly ciliated, and by 

 their vibration the little animal is capable of 

 swimming with great swiftness. 



With a slight exception, this is the infant stage 

 of all the marine Gastropoda, however diverse 

 the form of tlie adult. They all, therefore, undergo 

 a metamorphosis. The exception alluded to is that 

 of the Chitons, whose early stage, as recently shown 

 by the observations of Mr. Clark and Professor 

 Loven,^ is peculiar, and more resembling that of an 

 Annelid than of a MoUusk. In this case, the animal 

 can scarcely be said to undergo a metamorphosis ; 

 for the embryo, even within the Qg^, has nearly 

 the form of the parent, and the appearance of the 

 shell-plates is a matter of development. 



Localities, &c. — Almost every variety of shore, 

 and every range, from high-water mark to the 

 deep sea-bottom, is tenanted by some members of 



* See Ann. and Mag. of Nat. Hist, for Dec. 1855, and May 1856. 



