MOLXUSDA-r-f TEROPC/ECAi 



101 



of a small bladder. When this bladder bursts, the arm is 

 liberated. It is now considerably longer than the 

 others, and is provided with an oval plate at the 

 extremity, which is believed to be used, like the modi- 

 fied palpi of the male spiders, in conveying sperm to 

 the female. 



In the paper nautilus, this modified arm is detached 

 from the body of the male, and lodged in the mantle 

 chamber of the female, a fresh arm being from time to 

 time developed. When first discovered in this position, 

 it was believed to be an internal parasite, and received 

 the name of lieztocotylus (Gr. hekaton, a hundred ; kotulos, 

 a cup), because of its numerous sucking cups. 



CLASS 2. Pteropoda. 



135. The Pteropoda (Gr. pteron, a wing ; poda, feet) 

 are so called because their organs of locomotion consist of 

 two fin-like expansions of the foot (epipodia) placed 

 011 each side of the head. 



They are very small animals. 

 They swim near the surface, 

 sometimes in vast numbers, in 

 the deeper parts of the ocean. 

 The Clio Rorealis, a naked species, 

 not more than an inch in length, 

 forms the principal food of the 

 Baleen whale. 



Professor Huxley places the 

 Dentalium, which is common 

 enough on our own coasts, among 

 the Pteropoda. 



136. Skeleton. -The body is 

 covered with a mantle, which 

 generally secretes a univalve 

 shell of a glassy substance. This 



shell sometimes consists of two pieces united at the 



FIG. 42. HY ALE A. 



