136 



COMPARATIVE AX ATOMY. 



(Eunicidse, Fig. 56, A B), or are arborescent (Fig. 82, br) (e. g. in 

 the Amphinomeas). As a dorsal cirrus is frequently present in ad- 

 dition to these branchia?, they appear to be independent organs; 



Fig. 56. Diagrams of vertical sections of Annulata, showing the appendages. A Sec 

 tiou of Eunice. B of Myrianida. p Nemopodium. p ' Notopodium. br Branchia?. 



br 1 Cirri. 



this is the more probable since they frequently are separated from 

 the parapodia, and arise directly from the dorsal surface. 



They are distributed in varying number over the body. They are 

 sometimes found on all the segments of it, but they are gene- 

 rally less abundant at the tail (Eunice sanguinea, Amphinome). 

 Sometimes they are limited to a number of segments and become 

 gradually rudimentary (Arenicola, Hermella). In the tubicolous 

 forms, the mode of life leads to the development of the anterior, 

 and the disappearance of the posterior gills. On the three anterior 

 segments of the Terebellida) there are branched branchial tufts 

 (Fig. 70, br), in Pectinaria two comb-like branchia), and in 

 Branchiosabella and Sabellides simple filiform appendages at the 

 same point. 



In other divisions, also, of the Vermes the respiratory function is 

 assigned to processes of the body. This is true of the tentacles 

 of the Bryozoa. In the Gephyrea there are special developments as 

 respiratory processes ; in Sternaspis the hinder end of the body 

 carries vascular appendages. Finally, even in the Hirudinea there 

 are lamellar extensions of the integument arranged metamerically 

 (Branchellion). 



Integument. 



107. 



The integument of the Vermes, which is separated off from the 

 ectoderm, is closely united to the muscular system, by which it is 

 continued into the parenchyma of the body when a coolom is wanting". 

 This obtains in most of the Platyhchninths (Flat-worms) and Hiru- 

 dinea. Where the coclom is present, the integument, with the 

 muscles, forms a dermo-muscular tube, as in the Acanthocephali, 

 Gephyrea, and most Annulata. 



If we separate the dermo-muscular tube into its two constituen t 



