BY E. F. KALLMANN. 437 



are of very variable stoutness, occasionally attain to 100 // in 

 diameter, and are composed of roughly parallel spicules usually 

 not very compactly arranged. 8pongin appears to be entirely 

 absent. The microscleres are scattered chehe and sigmata, the 

 former rare except in the outermost layer of the dermis, the 

 latter fairly abundant and occurring only in the choanosome. 

 The dermal layer, which is never much more than 100 /x in thick- 

 ness, is provided with moderately abundant single spicules dis- 

 posed horizontally in several layers and crossing one another in 

 various directions. In the fistuhc, however, the dermal skeleton 

 (which is there the only skeleton) undergoes a gradual alteration 

 in its arrangement, and towards their extremities becomes a 

 reticulation of stout fibres. The meshes of this reticulation are 

 tympanised by a thin membrane, which is perforated with numer- 

 ous rounded pores varying from 15 to upwards of 80// in diameter. 



Spicules.- («.) The megascleres, which vary in form from tylota 

 to strongyla, the tylota being the more numerous, are nearly or 

 quite straight and scarcely, if at all, stouter at the middle than 

 towards the ends. The end-swellings of the tylota are elongate 

 and oblongish in shape, and, as a rule, are more pronounced in 

 the stouter spicules than in the slenderer. The very slenderest 

 (developmental) spicules are invariably strongyla, and usually 

 taper slightly from one end to the other. The maximum size of 

 the megascleres is 430 by 10/x, and their length seldom falls 

 below 320 /x. 



(6.) Isochelse arcuatse, 12*5 to 18 /x long, with the distal end of 

 the aljie pointed and abruptly incurved, and apparently with a 

 tooth-like prolongation of the tubercula. 



(c.) Simple and contort sigmata, 33 to 42 /x long from bend to 

 bend, and at most 3*5 /x stout. 



Embryos. — A few embryos of oval shape, the largest measuring 

 900 by 600 /x, were observed, most of which were provided with 

 spicules in the form of equal-ended tylota of size rarely exceeding 

 190 by 2 /x. The spicules were usually scattered throughout the 

 entire body of the embryo, but, in a few cases, were chiefly 

 collected in a loose bundle situated near one end. The largest 

 embryo without spicules measured 700 by 500//,, but others, of 



