68 THE BIOLOGY OF THE SEA-SHORE 



it seems improbable that the latter acts like a sucker as has 

 been suggested. Another view is that the animal is fixed 

 to the rock by means of a glutinous substance secreted by 

 its foot, but, from examination of specimens allowed to fix 

 themselves to plate glass, it seems that this view also is 

 unfounded. The most plausible explanation is that it is 

 a case of two very closely apposed surfaces, the foot being, 

 so to speak, rolled out on the rock." This is not the case 

 with the barnacle, however, whose powers of adhesion are 

 due to the presence of definite cement glands which have 

 been described at length by Darwin (185 1-4). The glands 

 with their ducts adhere to the basal membranes or shelly 

 plate and the secretion is shed all around the basis. The 

 cement issues either in a cellular condition, or, more 

 commonly, as a fine network which forms, at a short distance 

 from the orifices of the ducts, a fine sheet or layer which 

 has the capacity of occupying and filling up all inequalities 

 in the supporting surface. Darwin has seen it, when 

 spread over an encrusting Flustra, present an exact model 

 of every cell. In Coronula, a barnacle which is found on 

 the whale, the cement has the faculty of penetrating into and 

 almost blending with the epidermis of the Cetacean. The 

 area of attachment of sedentary shore animals seems to have 

 a similar capacity for fusing with the substratum, so that 

 many animals cannot be removed without damage. Probably 

 some chemical reaction takes place between the living tissue 

 and the substratum (of a similar nature to the dissolving 

 capacity of the roots of rock plants) so that the rock becomes 

 so intimately associated with the tissue as, for all practical 

 purposes, to become one with it. This is the case with 

 the Tunicates ; some species, e.g. the genus Pleurociona, lie 

 flat and are attached to large shells or other objects along 

 the greater part of the left side of the body. In some 

 cases, the test is prolonged, especially at the posterior end, 

 to form extensive expansions and stolon-like processes 

 (Herdman, 1889). 



Littoral Turbellarians are not only by their shape 

 particularly well adapted to withstanding wave-shock, but 



