/OOLOGY 



SECT. 



eye 



ink 



something in common with the string of proglottides of a Cestode, 



but differing radically, 

 as will be shown later, 

 in the mode of develop- 

 ment. Colour is very 

 general in the Turbel- 

 larian. though some are 

 transparent and colour 

 less. The most vivid 

 coloration characterises 

 some of the marine 

 Polyclads, the Khabdo- 

 coeles being compara- 

 tively obscure. The 

 surface is covered with 

 a coating of fine vibratile 

 cilia, the vibration of 

 which subserves respira- 

 tion as well as (in the 

 smaller forms) locomo- 

 tion. Among the ordi- 

 .fe nary cilia are frequently 

 disposed longer whip- 

 like cilia or flagella, 

 likewise motile ; and 

 sometimes non-motile 

 (sensory) cilia may 

 occur here and there. 



The Trematodes (Figs. 

 189, 202, 203, 204), 

 nearly related to the 

 Turbellarians in internal 

 organisation, resemble 

 them also in external 

 form, with certain modi- 

 fications connected with 

 a parasitic mode of life. 

 As in the latter class, 

 the leaf-shape prevails ; 

 an elongated form also 

 occurs, though more 

 nil-civ. The body is 

 usually thicker and more 

 solid than in most Tur- 



Eiu. 201. Gunda segmentata. Genera! view oi the bellai'ia. The anterior 

 organisation. lr. l>rain ; eye, eye; yen. up. genital , -,. 



aperture; int. intestine with its caeca ; long. ne. longi- end js QlStlDgUlP 



tuilinal nerve-cord ; ov. ovary; ood. oviduct ; pe. penis; r . i nci-m-mr 



;;/*. pharynx ; te. testes ; {. uterus. (After Lang.) 



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