Ii8 AN INTRODUCTION TO ZOOLOGY. 



the number of groups has been increased by the 

 division of the Radiata into Ccelenterata and Echino- 

 dermata, and of the Molluscainto three groups." The 

 above passage is taken from Glaus and Sedgwick's 

 "Text-book of Zoology/' in which nine chief divisions 

 of the animal kingdom are given. This is an essen- 

 tially practical classification, emphasizing the chief 

 great groups, without embodying any special theory 

 regarding their relations with one another, and includ- 

 ing under them certain animals that may be regarded 

 as connecting links {Balanoglossus, Ampliioxus). Some 

 prefer a classification that emphasizes the existence 

 of the links by placing them each in an important 

 division all to themselves, and throwing the linked 

 groups, together with the link, all under one larger 

 heading. A classification of this sort is much more 

 easy for the learner, because it makes sure that he 

 will not forget the importance and the meaning of the 

 links. 



The nine divisions alluded to are (in ascending 

 order), the Peotozoa, C(elenteeata, Bchinodermata, 

 Vjsemes, Aetheopoda, Molluscoidea, Mollusca, Tuni- 

 cata, and Veetebrata. By the other mode of classi- 

 fication which has just been referred to, the Veetebeates 

 or Ceaniata and the Tunicata or Ueochoedata, with 

 the link between them {Am]jliioKiis — group Cephalo- 

 choedata), and the link between them and Vermes 

 {Balanoglossus — group Hemichoedata), are placed 

 under the one great heading of Choedata. (See pp. 

 77, 78, 301.) It will be understood from this, that 



