8. THE TENTACULAR APPARATUS AND EXTERNAL DIGESTION 



85 



joined together for most of their length thus forming a permanent inter- 

 tentacular cavity. In the former genus it occupies the whole space inside the 

 long cylindrical crown (Fig. 58), while in the latter it makes a sort of spiral 

 cavity like the jam in a swiss roll (Fig. 59). An extraordinarily constant feature 

 which must be stressed is that in all species the pinnules project into the 

 intertentacular cavity where they form a densely interwoven tangle. 



Where adjacent tentacles touch one another rows of ciliated cells are found 

 (in the majority of species), and where the tentacles are fused into a tentacular 

 plate (in Lamellisabella and Spirobrachia) these cells form longitudinal 

 ciliated furrows (Figs. 57, 58, 59). 



Ш 



pi 



cav 



Fig. 58. Transverse section of tentacular crown of Lamellisabella zachsi. 



cav - intertentacular cavity; cil - ciliated band; сое - coelomic canal; cut -cuticle; nt - tentacular 

 nerve; pi - pinnule; tdd - right dorsal tentacle; tvd - right ventral tentacle; va- afferent vessel; 

 ve - efferent vessel. (After Ivanov, 1955b.) 



Respiration is undoubtedly one of the functions of the tentacular apparatus. 

 In no other aquatic animal, indeed, do we see either such a finely divided 

 respiratory organ or one with such a perfect blood system. To all appearances 

 neither the pinnules themselves nor their intracellular vessels is indispensable 

 for gaseous exchange, which may also be accomplished without their aid. It 

 is manifest that the whole apparatus of the tentacles carries out yet another 

 important function besides respiration. 



We are thus led to the conclusion that the tentacular apparatus serves in 

 addition for food collecting and digestion, and for absorption of the products 

 of digestion (Ivanov, 1955b). 



