VI THE VOYAGE OF H.M.S. CHALLENGER. 



until we are able to examine them microscopically, after an elaborate and troublesome 

 course of preparation, that the real interest of the sponge, namely, the minute anatomy 

 and histology of the soft parts, shows itself. It is probable that one of the chief causes 

 which have prevented the group from being hitherto almost entirely ignored is the 

 singular beauty of the spicules as "objects for the microscoiDC " ; now, however, many 

 observers have taken up the subject from a more scientific point of view, and we may 

 hope for a rapid advance in this department of science. 



Only within quite recent times have the Monaxonida begun to have a history of their 

 own apart from the history of sponges at large, and as the latter is a subject which has 

 already been more or less fully treated of by previous authors, such as Schmidt,^ 

 Vosmaer,^ and von Lendenfeld,^ we shall here mention only those facts which bear more 

 directly upon our group. 



To Zittel is due the credit of having first separated the Monaxonida from the 

 Hexactinellida and Tetractinellida, as a distinct group of siliceous sponges, under the 

 name Monactinellidae. This he did in 1878, in his paper Zur Stammegeschichte der 

 Spongien ; * where he proposes the following classification of the sponges : — 



Classe : Sponfjise oder Porifera. 



\. Ordnung : Myxospongix. Haeck. (Carnosa Cart.). 



2. Ordnung : Cei-aospongix. Bronn < ^ a .;. 



( (Psammonemata Cart). 



3. Ordnung: Monadinellids. Zitt. Kieselspongien mit einaxigen Nadeln. (Kaphidonemata, Ecliino- 



nemata und Holoraphidota z. Th. Carter). 



4. Ordnung : Tetractinellidx. Marshall. Kieselspongien mit aiikerformigen Nadebi oder mit den 



Nadeln des pyramidalen typus (Holoraphidota z. Th. Carter). 



5. Ordnung : Lithistidx. 0. Schmidt (Holoraphidota z. Th. Carter). 



6. Ordnung : HexadinelUdx. 0. Schmidt (Carter). 



7. Ordnung : Calcispongiee. Blv. (Calcarea Cart.). 



In 1883^ the name Monactinellid* was altered by SoUas to Monaxonidse, as the 

 former implied a viTong idea, viz., that the chief spicules of the group are " monactinal," 

 that is to say, consisting of only a single ray, while they are just as often " diactinal " or 

 composed of two rays diametrically opposite to one another. Both these forms of spicule 

 are, however, " monaxonid," that is to say they have each only one axis, which, in the 

 case of the diactinal forms passes through both the rays. Hence the slight alteration 

 in name appears to be justified. It has been further emended by subsequent writers 

 to " Monaxonida," as " ida3 " is the accepted termination for the name of a family. 



' Spong. Adriat. Meeres, p. 1. 



2 Article Porifera, in Bronn's Klassen und Ordnuugen des Thierreichs. 



3 Proc. Linn. See. N.S.W., vol. ix. pt. i., p. 122. 



* Festgabe der philosophischen Facultiit zum 50 jiihrigen Doctorjubilaum des Professor von Siebold, Miinchen. 



* Cassell's Natural History, 1883, vol. vi. p. 326. 



