38 Journal of the Mitchell Society. [March 



cavity of the sponge. In' Chonelasma similar septa have 



been observed. In HexactineUa labyrinthica skeletal masses 



of a reticular character, such as have been especially described 

 by Weltner, occur. In some cases such masses form layers 



separating- one part of the sponge from another. Possibly 



all these phenomena are pathological and similar, in so far 

 as they may indicate an effort of the sponge to shut off one 

 one part (diseased?) of the body from the rest. 



Morphology of spicules — variations and "pathological" con- 

 ditions. In Hyalonema pater if emm, pathological amphi- 

 discs such as have been observed by Marshall and Meyer and 

 F. E. Schulze occur. In these spicules several additional rays 

 of the hexact are developed. Certain details in the struc- 

 ture of the discohexasters of Caulopliacns schulzei suggest 

 that a hexaster may arise from a hexact through the develop- 

 ment of late?'al branches on the hexact rays. Another case 



is afforded by HexactineUa labyrinthica of what seems to be 



the degeneration of an uncinate into an oxydiact. In scop- 



ulae present in Sclerothamnopsis compressa, the arrangement 

 of the axial canals indicates that the spicule is equivalent to 



a branched diact, as Schulze has supposed. Abundant 



transitional forms indicate that the protriaenes of Thenea 



are modified dichotriaenes. In Thenea pyr if ormis a type of 



metaster is common which may be interpreted as transitional 

 between spirasters and euasters. — — In Penares foliaformis 

 peculiar dichotriaenes are found which approach the shape of 

 the lithistid phyllotriaene. The occurrence of pathologi- 

 cal branching oxeas is recorded for Petrosia. 



Variation. The variability of sponges in regard to points 

 of adult structure is universally recognized. O. Schmidt and 

 Vosmaer, in particular, have laid stress on the phenomenon 

 as bearing upon the problems of systematic classification. 

 The observations recorded in this report will fall under the 

 following heads: 



i. Variation in body-shape and general anatomy. 



Attention may be called to the difference in shape exhibited 



