22 E. KIRKPATETCK. 



there is the extremely fine square-meshed reticulum formed by the tangential rays 

 of the autodermal pentactins. Beneath this are subdermal spaces separated by the 

 proximal rays of the pentactins from the hypodermal network with its much larger 

 triangular or trapezoidal meshes. The strands of the hypodermal network are formed 

 of straight tangentially arranged bundles of rather thick diactins. The gastral region, 

 on the other hand, is without subgastral network and spaces, and the bundles of diactin 

 principalia are not distinguishable from those of the rest of the parenchyma. 



Canal- System and Soft Tissues. — The main exhalant canals run vertically 

 upwards from base to summit, receiving lateral branches in their course. A section 

 shows circles of the flagellated chambers opening into the finer canals. The subdermal 

 trabecular network, and the lining of many of the exhalant canals, are crowded with 

 masses of knollen-thesocytes, each thesocyte being about 8-1 0/x, in diameter. In 

 unstained balsam preparations these masses of thesocytes are clearly distinguished 

 by their dark yellow colour ; further, they take a deeper stain with borax carmine 

 than do the rest of the sponge tissues. 



The skeleton is formed mainly of bundles of diactins and of separate large 

 hexactins, pentactins, stauractins, and tauactins. 



Spicules. — The principalia are diactins which vary considerably in length and 

 thickness, the average kind being about 7560 X 22ju,, tapering to fine points and 

 spined at the extremities. The spicules, which, in specimen A, are regarded as possible 

 marginalia, are in the form of two or three long curved diactins about 5 cm. in length. 

 They have become misplaced, and possibly may not belong to the sponge. The delicate 

 marginalia in specimen C project about 6 mm., and are about 13 mm. in length. 



The little tufts of diactin basalia are about 2 ■ 5 cm. in length. 



The large regular hexactins (V. 2a) have rays 800 x 60/a, slightly spined at the 

 ends ; large pentactins, stauractins, and tauactins (V. 2b, c, d) also are present. 



The autodermalia (V. 2e) are pentactins with rays 172 x 24-5/1,, closely spined. 

 Young pentactins with fine, smooth, sharp rays occur both in the dermal and gastral 

 layers. 



The autogastralia are mostly pentactins similar to the autodermalia ; a few small 

 regular hexactins also occur, especially in specimen C. Plate V., figs. 2f-2f , shows 

 several modified hexactins and a pentactin from the region round the single exhalant 

 orifice in specimen C. 



The intermedia. Oxyhexasters. Holoxyhexasters (V. 2g), 197/a, with bifurcate 

 primary rays, short or almost absent, are not uncommon ; a kind (V. 2g^), 86)u., in 

 which each primary ray ends in a disk, whence five to six sharp-pointed secondary rays 

 diverge, occurs less frequently. 



Hemioxyhexasters (V. 2g^), about 180/i, are abundant; and monoxyhexasters 

 (V. 2g^), also about 180 fj. in diameter, occur, but rarely; fig. 2g^ shows a hemi- 

 oxyhexaster in which one of the secondary rays has a trifid termination. (The small 

 " 2." of 2g^ has been omitted in the plate.) 



