AND THE LOWER ANIMALS. 107 



length of time, however, the adherent muscles become 

 detached, and the animal leaves the dwelling which it 

 inhabited since its birth; its body is elongated; the 

 foot having cast off its operculum, which is now useless, 

 begins to discharge its real function, and on the other 

 hand, the rotatory apparatus becomes atrophied ; the 

 stomach is prolonged backwards as a cul-de-sac, which 

 rapidly increases in size, and sends off ramifications ; a 

 pair of appendages is seen upon the dorsal surface : 

 these are soon followed by others, and eventually the 

 larva, which at first resembled that of an ordinary 

 mollusk, becomes a true phlebenterate. 



The embryogeny of gastropods has been the subject 

 of several works ; and among those who have helped 

 to clear up that branch which we are considering, we 

 find the names of some of our most distinguished con- 

 temporaries ; * but it is not the same with the Acephala 

 or bivalve mollusks. The only researches upon this 

 subject, in addition to those already mentioned, are, so 

 far as I am aware, Loeven's great work, some essays 



* The first researches upon the development of gastropods are 

 those of M. Stiebel, a German naturalist, and are dated 1815. 

 Among those who have since devoted themselves to the subject, I 

 may mention the names of Allman, W. B. Carpenter, Cams, 

 Danielsen, Dumortier, Frey, Grant, Jacquemin, Koren, Klark, 

 Lacaze du Thiers, Laurent, Leydig, F. Miiller, Loeven, Nordmann, 

 Pouchet, Prevost, Kathke, Reid, Saars, Von Siebold, Van Beneden, 

 Vogt, Windischmann, &c. The earlier writings of these naturalists 

 were devoted to the terrestrial and fresh-water species, and conse- 

 quently the metamorphoses of the marine classes remained for a 

 long while unknown. In 1827, the English naturalist Grant dis- 

 covered the rotatory apparatus and pointed out its function ; 

 but it was not until the year 1837 that M. Saars, a clergyman of 

 Berghem, made known the important fact that the larvae of naked 

 mollusks are provided with a distinct shell. 



