THE SPONGES. 7 



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

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

 spicules of Hyalonemia ; BatJujdorus, p. 47, attached to root spicules of Ht/a- 

 lon&ina and to stalks of Caiilophacus or similar sponge. 



Morphology in general. Further evidence of a convincing character has 

 been gained that the complex Eurete and Farrea 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 two Tetractinellid genera, Poecillastra and Penares, pp. 

 99, 103, 109. 



Pathological 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 Hexadinella lahyrinthica 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 '^ pathological" conditions. In Hga- 

 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 Caidophacus schidzei suggest that a 

 hexaster may arise from a hexact through the development of lateral 



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



Hexadinella lahyrinthica of what seems to be the degeneration of an uncinate 



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



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

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

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

 fied dichotriaenes, p. 85. In Thenea pyrifonnis a type of metaster is 



common which may be interpreted as transitional between spirasters and 

 euasters, p. 96. In Penares foUaforniis peculiar dichotriaenes are found 



