RHABPOCALYPTUS UNGüICüLATUS. 271 



The subdermal sj^ace presents itself as a rather conspicuous 

 layer in sections of the wall. In places it is as much as 3 mm. 

 across. It is traversed by the pillars which join the ectosome to 

 the choanosome and consist mainly of the shafts of prostal and 

 hypodermal pentactins and of their comitalia. The appearance 

 of the wall in section partakes much of that which I have figured 

 from R. capUlalus in PL XXII. , fig. 12. 



As to the roundish apertures of the incur rent canals a certain 

 différence is noticeable with respect to their size and manner of 

 distribution on the two lateral sides. On the side shown in PL 

 XXL, fig. 1, some of them measure up to 7 mm. in diameter, 

 and lie promiscuously with others which are at most about half, 

 and often much less than half, as wide. On the other side the 

 apertures are of a more uniform size, mostly measuring 3-5 mm. 

 in width and situated somewhat more closely together. 



The gastral surface is covered over by a continuous gastral 

 lacework, the regularly quadrate meshes of which are plainly 

 visible to the naked eye. They are much larger than in R. mollis 

 or R. capillalus, measuring i-h mm. in length of sides. In the 

 interspace between the excurrent canalar apertures, the layer is 

 in tolerably close contact with the choanosome; over the apertures 

 it frequently heaves up in a vault-like manner. Kemarkable is 

 the fact that even over the largest apertures there are seen no 

 hypogastral strands in suj^port of the gastral layer. 



The excurrent canalar apertures in most parts of the 

 gastral cavity are rather closely set, reaching up to 5 or 6 mm. 

 in diameter. In the bottom of the cavity some of them are as 

 wide as 8 mm. 



