80 



PART I. GENERAL ACCOUNT 



cca 



va сое 



Fig. 53. Pari of a transverse section of a tentacle of Latnellisabella zachsi ( I), and sections of ten- 

 tacular pinnules of the same species: И longitudinal section of the ilistal end of a pinnule; 

 С transverse section of two adjacent pinnules; and I) transverse section of a pinnule with 

 the capillaries full of blood. 



cc — ciliated cell; cca cell adjacent to capillar) ; eg gland cell; cat coelomic canal; cut cuticle; 

 <■/> epidermis; nib basement membrane; ml longitudinal muscle fibre \nu nucleus of pinnule; 

 per peritoneum; va afferenl vessel of tentacle ; vap afferent capillary of pinnule; ve efferent 

 vessel of tentacle; ;<■/> efferent capillary of pinnule. (Alter tvanov, 1960a.) 



Each pinnule represents a single cylindrical epidermal cell, projecting far 

 beyond the surrounding epidermis, but with the nucleus near the base within 

 the thickness of the epidermis proper. Its surface is covered by the finest 

 imaginable cuticle. The homogeneous cytoplasm of the pinnule is pierced by 

 two long thin parallel canals, which, however strange it may seem at first 

 glance, are nothing less than intracellular blood vessels and are often found 

 filled with the characteristic small blood granules (Fig. 53/)). These capil- 

 laries run the whole length of the cell to join near the tip of the pinnule 

 (Fig. 55). They possess their own walls formed of a very thin structureless 

 intima. A thin membrane of the same substance links the walls of the two 

 capillaries and forms a sort of longitudinal ribbon up the centre of the 

 pinnule (Fig. 53C). Quite obviously one of these capillaries must be the 

 afferent and the other the efferent vessel of the pinnule. 



