24-2 



ARCHI ANNELID A 



K 



" primitive." It is quite possible, and even probable, that Dint 

 philus is ancestrally simple ; whilst many features in Polygordw 

 appear to be the result of simplification. For this reason it 

 would be well to separate Dinophilus from the other two genera 

 on account of its much less elaborate and more generalised striu 

 t ure> so generalised, in fact, that the worm is by some authorities 

 placed amongst the Planarians ; for the present, however, the 



Fig. 121. Dinophilus taeni- 

 atus. (FromHarmer.) The 

 left figure represents the 

 dorsal surface of a young 

 individual, x 76 ; the 

 mouth and alimentary tract 

 are seen by transparency : 

 p, prostomium, with two 

 bands of cilia and a pair 

 of eyes ; a, anus ; t, tail ; 

 1 to 5, the segments with 

 ciliated bands. The right 

 figure shows the anatomy 

 of the male, x 38 : b, 

 rectum ; c, body -cavity ; 

 d, vas deferens ; m, 

 muscular organ (pharynx) ; 

 n', the first nephridium ; 

 oe, entrance to oesophagus ; 

 p, penis ; st, intestine 

 (stomach) ; s.x, seminal 

 vesicle (5th nephridium). 



group Archiannelida may be regarded as containing three genera : 

 Dinophilus, Protodrilus, and Polygordius} 



Dinophilus is represented on our coasts by at least two 

 species : D. gigas Weldon 2 and D. taeniatus Harmer. 3 The 

 latter is about one-twelfth of an inch in length, bright orange in 

 colour, and more or less abundant, at springtime, in the rock 

 pools around Plymouth, where it may be found amongst green 

 algae, or on the mud at the bottom of the pools. 



1 Another worm, Histriobdella (Histriodrilus) homari, which is parasitic on the 

 eggs of the lobster, and which occurs on our coast, has been placed amongst the 

 Archiannelida. It is a minute form, with peculiarities in its anatomy which render 

 its affinities uncertain. 



2 Quart. J. Micr. Sci. xxvii. 1887, p. 109. 



3 J. Mar. Biol. Assoc, vol. i. (n.s.) 1889-90, p. 119. 



