MOLLUSCA. 7 



Child. No, for when a snail is trodden upon, 

 a white fluid issues from it ; is this its blood ? 



Teacher. Yes, it may be considered as a kind 

 of blood. How does it differ from that which 

 circulates through our bodies ? 

 Child. It is white and cold. 

 Teacher. True ; and in consequence some 

 naturalists have not considered it as blood, and 

 have described the mollusca to be exsanguin- 

 eous ; a term signifying without blood, and 

 derived from Latin ex 9 out of, and sanguine, 

 blood. As this fluid flows through their bodie.s 

 in vessels issuing from their hearts, it is now 

 generally called their blood. What are you 

 watching in the snail ? 



Child. The very quick manner in which it 

 draws in its horns, and shrinks into its shell, if 

 it is touched. 



Teacher. What would you determine with 

 respect to the animal from this circumstance ? 

 Child. That it has the sense of feeling. 

 Teacher. Yes ; and which part appears most 

 sensitive ? 



Child. The horns. 



Teacher. And do you observe how the little 

 animal feels about, and tries with these projec- 

 tions which you call horns ? They have from 

 thence been termed Tentacula 9 from the Latin, 

 tentare, to try or feel. How many tentacula have 

 snails ? 



Child. Four. 



Teacher. The tentacuia vary in number ; 



