L.M.H.C. TURBELLAlilA. 75 



enables it to adhere so strongl}^ to the substratum of which 

 it appears to form an integral part, that it is often necessary 

 to use a knife to detach the specimens. Professor Lang 

 has observed numerous examples at Naples and these 

 appear to be adapted each to its particular and self-coloured 

 surroundings. 



While these facts, the striking nature of which can only 

 be realised on the shore, appear to point to detailed 

 adaptation in the form, texture, colour, and innnobility of 

 the Polyclad to the Ascidian, there are one or two opposing 

 facts which must not be omitted in attempting to arrive 

 at a just conclusion. Cycloporus is sometimes found on 

 substrata, with which it has no perceptible resemblance 

 and secondly 3 — 5 black spots are generally present in 

 var. laevigatus which have no analogue in the ascidian. 

 This only helps to shew how very fragmentary and 

 incomplete is our knowledge of the true life-relations of 

 these animals. A theory, thoroughly consistent with the 

 facts cannot be framed until far more observations than w^e 

 at present possess, are made in different localities and at 

 different times of the year. 



Certain colour-varieties of Cycloporus papillosus closely 

 resemble Stylostomum variabile, and it may be useful to 

 point out the features by which the former can be always 

 recognized. The presence of a median gut-branch over 

 the pharyngeal region is diagnostic. Such a branch only 

 exists in front of that region in Stylostomum. Again, 

 examination of hving or still better, of well-preserved 

 specimens of Cycloporus, shews that the mouth-opening is 

 distinct from the male- and female genital apertures. In 

 Stylostomum on the other hand, the male and oral aper- 

 tures are united and open just behind the brain. 



Cycloporus papillosus has been observed by Prof. 

 Herdman at Pufhn Island, and was dredged by Mr. H. 



