LESSONS IN ZOOLOGY. 289 



nautilus, cuttlefish and other interesting mollusks belong to this 

 class. Some attain great size and strength, so that with their 

 long arms, supplied with powerful suckers, they sometimes de- 

 stroy men, and so fierce and destructive are they that one group 

 has received the name of devil fish. 



The Molluscoidea. The bryozoa and brachiopoda, now 

 grouped as molluscoidea are interesting animals whose relations 

 are not well made out, and which do not appear much alike, but 

 a study of their developmental history seems to show them 

 closely related. The bryozoa are small animals usually united 

 together forming colonies so as to present the appearance of 

 sprigs of moss. There is no vascular system, and the nervous 

 system consists of a simple ganglion. The mouth, surrounded 

 by a crown of tentacles, leads to a capacious stomach, the intes- 

 tine terminating near the mouth. The brachiopoda are fixed ani- 

 mals of larger size, having a shell consisting of dorsal and ven- 

 tral valves. A vascular system is present, and the nervous 

 system is a ring about the oesophagus with two ganglia in it. 

 The mouth is provided with two long, coiled arms, which serve 

 as a respiratory apparatus, and aid in gathering food for the 

 animal. The oldest fossils belong to this group. 



The Tunicata. These are saccular or barrel-shaped animals, 

 whose respiratory cavity has two wide openings, between which 

 is placed the simple ganglion which constitutes the nervous sys- 

 tem. Judging from the development of the different systems of 

 organs the ascidians would appear to take low rank in the scale 

 of being, but a study of their embryonic development seems to 

 show that they have close relations to the lower vertebrates. 

 They are nearly all marine animals of little or no economic 

 value, and of no special value for study by beginners in zoology. 



L. S. 19 



