UNIVALVE MOLLUSCANS. 301 



young of other shell-fish. They form an im- 

 portant article of food to some African nations. 



Before I close this account of these preda- 

 ceous Molluscans, I must observe, that they 

 have two distinct sexes, and consequently male 

 and female shells. The genuine hermaphrodites 

 are confined to the bivalves, for in the univalve 

 hermaphrodites two individuals are necessary 

 for re-production, and therefore those form a 

 distinct link between the true hermaphrodites 

 that impregnate themselves, and those that have 

 distinct sexes. So gradual are the steps by 

 which the Creator passes from low to high. 

 First, animals are re-produced without sexual 

 intercourse, as in the polypes ; then the two 

 sexes are united in one body, and suffice for 

 their own impregnation next follow two sexes 

 in the same body, which cannot impregnate 

 themselves, bringing us at last to distinct sexes, 

 or unisexual individuals. 



4. Lamarck's fifth family, the Heteropods, I 

 introduce here because, being univalves, they 

 appear to connect that tribe with the Cepha- 

 lopods forming his fourth order, but which from 

 the discovery of the animal of Nautilus Pom- 

 pilius, so admirably described by Mr. Owen, 

 being further removed from the other Mollus- 

 cans, and the animal of the Heteropods having 

 a proboscis and only two tentacles, seems inter- 



