SPECIAL PROBLEMS OF SHORE LIFE 69 



they are provided, in addition, with special means of attach- 

 ment. In Convoluta paradoxa the " tail " or pointed hinder 

 end of the body is provided with sticky adhesive papillae 

 which enable it to remain firmly attached to its favourite 

 weed {Ceramium sps.). These papillae are elevations of 

 the epidermis. Gamble (1893) has roughly estimated their 

 power of adhesion by the use of a powerful syringe. Re- 

 peated action of an in-going or out-going stream does not 

 affect the Convoluta. It merely sways slightly in the 

 direction of the current without in the least loosening its 

 hold on the substratum. This device, according to the same 

 writer, is general among littoral Turbellaria ; some forms 

 indeed {e.g. Planaria dioica) are provided with adhesive 

 papillas over their entire surface. 



A similar method of adhesion has been observed in the 

 Nudibranch Ancula cristata. This is a very slimy species. 

 Herdman and Clubb (1892) state that " in the natural state the 

 mucus is chiefly on the foot and especially at the posterior 

 end, each individual having a slimy string attached to the end 

 of the tail by which it is anchored. This no doubt accounts 

 for the manner in which the animal is able to live on exposed 

 rocks in the wash of the tide. We have several times 

 watched specimens of Ancula in a few inches of water where 

 there was a strong tide running past the rocks and the 

 waves were dashing on them and noticed that they were 

 swayed backwards and forwards in the water but were 

 securely anchored by their tails." 



In a number of common shore fish, e.g. species of 

 Liparis, Gobtus, Cyclopterus, the pelvic fins have become 

 partially or completely modified as suckers. Speaking of 

 the function of the suckers in young individuals of Cyclo- 

 pterus, MTntosh (1896) says these fishes " adhere to the 

 blades of the tangles and other seaweeds and in the mazes 

 of these find that safety from the ready application of their 

 suckers which would be denied them in the open sea." 



Aflalo (1904) makes a similar statement in regard to 

 species of goby : " the ventral fins of these gobies show the 

 transition to the disc of the ' suckers ' and many of these fish 



