140 ART. 7. — I. IJIMA : HEXACÏINELLTDA, IT. 



Figs. 16 and 17, PI. XI., show in natural size the appearance 

 of the endosomal and the ectosomal layer respectively. A close 

 familiarity with the characters of either will be sufficient to enable 

 one to recognize the species even if the specimen to be determined 

 1)6 a small fragment, provided of course one or the other of the 

 layers is well preserved. 



In the ectosome (PI. XIL, fig. 34) the extremely delicate 

 dermal layer exhibits minute quadrate meshes, just discernible as 

 such with tlie naked eye. JNIuch more distinct is the hypodermal 

 latticework (see PI. XL, fig. 17), the meshes of which are triangular, 

 trapezoidal or polygonal in shape and measure rarely over 2 ram., 

 but far more frequently less than 1 mm., in the length of their 

 sides. Towards the ajDcx of the cones the hypodermal beams 

 converge more or less from all sides, making the meshes between 

 them narrower Init more elongate than in other joarts. The 

 beams may measure up to 130 /^ in breadth. They are therefore 

 not very thick, but still are thick enough to be distinctly perceived 

 with the unaided eye. The points of intersection often appear 

 somewhat thickened in a node-like manner, owing to dense 

 concentration there of the soft parts. The subdermal space in the 

 intervals between the incurrent canalar apertures may be as wide 

 as 1 mm. It is traversed by numerous strands, the pillars, con- 

 necting the ectosome to the choanosome. The apertures of the 

 incurrent canals are of various sizes. In the larger specimens, 

 the largest canals may reach 4 mm. in diameter but are in general 

 much smaller. 



The gastral surface is on the whole tolerably smooth, though 

 it may sometimes exhibit a wrinkled appearance. The canalar 

 apertures on this side of the wall are on the whole larger, but 

 necessarily less in number, than those on the external side of the 



