152 



ACTINOZOA. 





free by the gaping of the cell itself, around the 

 thread's distal extremity. 



On the whole it seems safe to say that anion* the 

 Achnozoa the thread-cells exhibit a greaterten- 

 dency to become collected in particular organs than 

 has been shown to be the case with the Hydrozoa • 

 though we by no means wish to forget the tentacles 

 or nematophores of the latter. The mesenteric 

 cords of the Sea-anemones strikingly illustrate 

 this, and, in the Ctenophora, the urticating organs 

 form a well marked layer on the outer surface of 

 the tentacles and their lateral fringes. Parallel to 

 and agreeing in position with, these last, the two 

 tentacles m Hormiphora are furnished, as Ge^en- 

 baur has proved, with a number of very peculiar, 

 bright yellow, appendages, one between from about 

 every ten to fifteen of the ordinary side filaments. 

 -kach of these bodies, which serve as special recep- 

 tacles for the thread-cells, is hollow, of a flattened 

 fusiform, or lancet-shaped, form, with a short stalk 

 of attachment, above which it is prolonged later- 

 ally into several pairs of tubular processes, which 

 gradually diminish in length, and finally vanish 

 altogether, before reaching its free, simply taper- 

 ing, extremity. J 



Pigment-masses, irregularly scattered in some 

 Achnozoa, are in others combined so as to form 

 more or less definite layers, which may readily 

 be examined in the commoner species of Sea- 

 anemones. In the substance of the body-wall 

 and tentacles, outside the muscles of the mesen- 

 teries, or even in the digestive tube itself, such 



interrupted layers of colouring-matter have been 

 observed. 



The exquisite roseate tint of some Ctenophora 





