252 



ZOOLOGY 



SECT. 



eye 



Icnq ne. 



int 



ovd- 



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 Ehabdo- 

 cceles 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- 

 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 

 rarely. The body is 

 usually thicker and more 

 _ solid than in most Tur- 



Fio. 201. Gunda segment at a. General view of the bellaria. The anterior 



organisation, br. bruin; eye, eye; yen. ap. genital 



aperture ; int. intestine with its ctvca ; Jong. ne. longi- end IS 



tudinal nerve-cord ; or. ovary ; ovd. oviduct ; pe. penis ; r rrtT +> 



ph. pharynx ; te. testes ; ut. uterus. (After Lang.) lrom t 



rrtQfoMr ^r 

 pOSteriOT by 



