THE SPONGES. 7 



Pacific. Some of the Hexactinellids from great depths have been found to 

 live clustering upon one another : Caulophacus, pp. 39, 46, attached to root 

 spicules of Hyalonevia ; Batlnjdorus, p. 47, attached to root spicules of Hya- 

 lonema and to stalks of Caulophacus or similar sponge. 



Morpliology in general. Further evidence of a convincing character has 

 been gained that the complex Enrete and Farrm colonies are derived onto- 

 genetically from simple cup-like forms, pp. 60, 61, 66. The close simi- 

 larity between the main afferent and efferent canals and their apertures in 



Poecillastra tricornis is worthy of remark, p. 97. The observations of 



Sollas and of Dendy on the occurrence of a peculiar fenestrated membrane 

 (Sollas's membrane) in the flagellated chambers of certain sponges have 

 been confirmed for tv/o Tetractinellid genera, PoeciUastm and Penarcs, pp. 

 99, 103, 109. 



Pailiological phenomena in general. In Euplectella skeletal septa of a 

 reticular character have been found crossing the cavity of the sponge, 



p. 29. In Chonelasma similar septa have been observed, p. 70. 



In HexacUnella labyrinthica skeletal masses of a reticular character, such as 

 have been especially described by Weltner, occur, p. 75. 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 part (diseased?) 

 of the body from the rest. 



Morphology of spicules — variations and '■^ pathologicaV conditions. In llya- 

 lonema patcriferum, pathological amphidiscs such as have been observed by 

 Marshall and Meyer and F. E. Schulze occur. In these spicules, p. 28, 



several additional rays of the hexact are developed. Certain details in 



the structure of the discohexasters of Caulophacus schiikei suggest (hat a 

 hexaster may arise from a hexact through the development of lateral 



brandies on the hexact rays, pp. 44, 45. Another case is afforded by 



Hexactinella labyrinthica of what seems to be the degeneration of an uncinate 



into an oxydiact, p. 77. In scopulae present in Sclerothamnopds com- 



pressa, the arrangement of the axial canals indicates that the spicule is 

 equivalent to a branched diact, as Schulze has supjjosed, p. 82. Abun- 

 dant transitional forms indicate that the protriaenes of Thenea are modi- 

 fied dichotriaenes, p. 85. In Thenea pyrifonais a type of nietaster is 



common which may be interpreted as transitional between spirasters and 

 euasters, p. 96. In Pciuircs foliaformis peculiar dichotriaenes are found 



