348 A.. T. MASTERMAN. 



ing direction (figs. 1,9^ 14), — cf. Mcintosh (3). They originate 

 from the thickened chondroid skeleton lying between the 

 posterior coelomic wall of the epistome and the anterior wall 

 of the collar, and run forwards and outwards to be inserted 

 into the thin chondroid tissue immediately underlying the 

 anterior nerve-ring of the epistome (PI. 25, fig. 15). Their 

 contraction would result in the drawing inwards of the central 

 ])art of the epistomial ventral surface ; and hence, if this organ 

 were applied to a flat surface, they would convert it into an 

 efficient sucker. 



The ccelomic cavity of the collar and plumes is also traversed 

 by a number of protoplasmic filaments which are much finer 

 than those of the epistome ; they may or may not be contrac- 

 tile (figs. 15, 16). In all cases they run from one part of the 

 chondroid tissue lining the coelom to another, and appear 

 indefinite in arrangement. The largest and best defined run 

 from the lateral skeletal bodies to the head of the notochords 

 (fig. 15). 



In the trunk there is (contrary to Phoronis and Balano- 

 glossus) a marked absence of muscular tissue, with the 

 exception of the mid-ventral region, in which there are definite 

 muscular bands running from behind the mouth to be inserted 

 into the "ventral sucker " (PI. 25, fig. 17, v.m.), as described 

 by Mcintosh. In the ventral sucker itself these muscles show 

 a fibrous structure. 



Skeletal System. — Closely underlying the ectodermal cells 

 is found the so-called " basement tissue,'^ which varies greatly 

 in thickness in various parts. A thin layer of this tissue lines 

 the whole cavity of the epistome, and where its mesodermic 

 wall is in contiguity with that of the collar coelom there is 

 formed on either side (fig. 15) a thick mass of the same tissue, 

 from which long muscular fibres run forwards through the 

 epistomial ccelom and backwards to the front end of the 

 notochords. They have been referred to as the lateral skeletal 

 masses. 



The chondroid tissue is also easy to trace in the collar region, 

 — in the post-oral lamella, the plumes and pinnae, and the 



