72 CALYCOSILVA CANTHARELLUS. 



helonychhexasters (in C. c. var. helix only) ; and plumicomes (exceedingly scarce 

 in C. c. var. megonychia) . 



In the body proper of the sponge all the spicules are isolated and free. 

 In the stalk the ordinary choanosomal rhabds are joined to form a dictyonal net- 

 work to which also a few hexactines may be attached. 



In C. c. var. simplex (B) the skeleton-net of the stalk (Plate 5, figs. 3b, 10) 

 closely sm-rounds the hyalonematid root-tuft spicule (Plate 5, figs. 3, 10a) 

 which forms the base of attachment. The thinner distal end of this envelope, 

 which corresponds to the lower end of the stalk, consists of a network with 

 beams 12-35 /x thick, and irregularly triangular or polygonal meshes, on an 

 average about 100 ^ wide. In this network main longitudinal and secondary 

 transverse beams cannot be distinguished. Farther on, towards the upper end 

 of the stalk, the network becomes more regular and more and more distinctly 

 composed of longitudinal main beams (15-65 fi thick, usually 20-45 m), joined 

 by short, transverse connections to a ladder-like structure. In consequence 

 of the main beams not being quite parallel, and the transverse beams very irregu- 

 larly distributed, the meshes of this part of the network are very unequal in size, 

 5-50 /J. and more broad, 30-200 yu and more long. However different their 

 size may be, in shape and position these meshes are very much alike, always 

 elongated, oval, or rectangular with strongly rounded corners, and arranged with 

 their long axis extending longitudinally. In some parts of this network the 

 beams are smooth, in others covered by small, low, sharp spines. At the upper 

 end of the stalk the transverse connections become less numerous and the net- 

 work dissolves itself into a sheaf of longitudinal rhabds. 



Ends of the rhabds taking part in the formation of the net in many places 

 freely protrude from it. These free rhabd-termini, which are rather scarce 

 below, but become quite frequent above, are blunt-pointed or rounded, and 

 just below the end, for a distance of 50-70 n, densely covered with fairly large 

 spines. In the blunt-pointed ones the end itself is free from spines. In the 

 terminally rounded ones the spines cover the end also. The spined part below 

 the end, particularly in the blunt-pointed forms, is considerably thickened, club- 

 shaped, and measures 15-28 ^ in transverse diameter. 



The skeleton-net in the stalk of C. c. var. helix (Plate 5, figs. 5, 7) is similar, 

 but smooth and still more ladder-like. Its beams are 10-53 m, usually 20-40 /i, 

 the free ends of the rhabds taking part in its formation, 15-30 fi thick. At the 

 upper end of the stalk the transverse beams become scarcer and the character- 

 istically tubular network dissolves itself into a hollow sheaf of isolated longi- 



