PLACOSOMA PAKAt)ICïYUM. 11 



the fact that the subjacent chamber- layer shows the Inline! chamber- 

 ends all directed towards it, similarly as on the convex side 

 (Chall. Eep., PL L., iig. 1). It is then plain that the inflow of 

 Avater takes place all over the surface of both sides, except ot 

 course at the separate excurrent oritices on the concave side. Ihe 

 condition uf this side then exactly corresponds to that on the 

 back of Placosoma paradictyu/n, while the convex side may be 

 said to correspond to the front, though it lacks a special structure 

 like the frontal lattice. 



Spiculation. 



(PI. IL). 



First let me complete an account of the spiculation in the 

 sponge- body proper. 



Of the parenchymalia the predominating form is a line 

 diactin, generally 2-8 mm. in length. The breadth, not exceed- 

 ing 15 y, remains nearly the same throughout ; not seldom 

 however it slio'htlv increases towards both extremities. These 

 are usually bluntly pointed ; the surface near them is nearly 

 smooth or obsoletely rough on account of insignificant tubercles. 

 The center of the diactins is generally quite smooth, and 

 exceptionally marked by an annular swelling or by knobs in 

 cruciate arrangement. The diactins are disposed partly irregular- 

 ly or in loose indefinite groups and partly in long, compact 

 and thread-like fascicles of variable strength (PL II., fig. 15). 

 The hypodermal beams of the frontal lattice (see fig. 13) are 

 nothing else than extensions of such parenchymal fascicles from 

 the choanosonie. — Among the parenchymalia making up the 



