L.M.B.C. TURBELLARIA. 169 
enables it to adhere so strongly 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 immobility 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 83—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 we 
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 living 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 Puffin Island, and was dredged by Mr. H. 
