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 among the 

 Actinozoa the thread-cells exhibit a greater ten- 

 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 in Hormi'phora are furnished, as Gregen- 

 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. 

 Each 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. 



Pigment-masses, irregularly scattered in some 

 Actinozoa, 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 



