BY WILLIAM A. HASWELL. 337 



The epidermis (plate XXVI I. fig. 15) is a very thin layer save in 

 certain situations, only reaching a considerable development on the 

 praestomiurn and part of the peristomium, the grooves of the 

 tentacles and the branchial filaments. Beneath each of the 

 papillae the epidermis becomes modified as described below. It 

 consists of flattened cells (fig. 16) of polygonal outline, the reticu- 

 lated protoplasm of which presents smaller and larger vacuoles. 

 The reticulated substance of neighbouring cells is separated by 

 narrow uncolourable bands, which anastomose and present the 

 appearance of a branching system of fine channels, which may be 

 connected with the secretion of the mucus. 



Like the adherent layer of mucus the papillce are specially 

 characteristic of the Ohloraemidae, and appear to be present in 

 one form or another in all the members of the family. They 

 have been described under various names, " mucus-secreting 

 papillae," " poils," "tubercles," "granules." They attain their 

 greatest development as regards length in Sijyhonostomum, where 

 they are greatly elongated, so as to penetrate to the surface 

 through the relatively very thick layer of mucus. In Coppingeria 

 (plate xxvn. figs. 11-14) they occur over the entire surface of the 

 body, giving it a very remarkable appearance when examined 

 with a lens, owing to their resemblance to the tube-feet of a 

 sporadipodous Holothurian. They are not of uniform length, 

 but vary considerably in this respect, a fact which might be apt 

 to produce the erroneous impression that they are extensile and 

 retractile. They are specially developed around the bases of the 

 cephalic setae, where they attain a length of as much as 3 or 4 mm. 

 In other parts they are much shorter, on an average -5 mm. in 

 length. Their form is subcylindrical, with a slight terminal knob- 

 like enlargement ; in the shorter forms there is usually a consider- 

 able amount of constriction at the base, and in these also the apex 

 is pushed in to form a shallow cup-like concavity, which may, 

 however, though very regular, have been produced, or at least 

 increased, by the action of the alcohol. 



The memoirs of Delle Chiaje not being at present accessible to 

 me, the earliest detailed account of these papillae which I have 



