( 4104 ) 
Zoology. — “On the Shape of some Siliceous Spicules of Sponges” ; 
by Dr. G. C. J. Vosmarr. 
The perplexing amount of variety exhibited by sponge spicules 
has since long made it desirable 1°t to designate certain spicules by 
special terms, and 2rd to divide the spicules into groups. The first 
attempt to such a classification was made by BOWERBANK in 1858 ; 
later, in 1864, modified by the same author. BowerBANK divided 
(1864 p. 13) the spicula into “essential skeleton spicula” and “auxiliary 
spicula”. It is obvious that this primary classification is not based 
on morphological characters. Since KOLLIKER (1864) has pointed out 
the morphological value of the axial canal or, more correctly, the 
axial thread (“Centralfaden”), Oscar Scumipt has rightly based his 
classification of siliceous spicula on the presence of one or more of 
such axial threads, which after all represent the axes of the spicula. 
Scumipt distinguishes (1870 p. 2—6) four types of spicules: 
1. „Die einaxigen Kieselkörper.” 
2. Die Kieselkörper, deren Grundform die dreikantige reguläre 
Pyramide.” 
3. Die dreiaxigen Kieselkörper.” 
4. Die Kieselkörper mit unendlich vielen Axen.” 
Neither Gray (1873, p. 203— 217), nor Carrer (1875, p. 11—15) 
understood the fundamental value of Scumipt’s classification. My 
attempts to draw attention to it (1881 a and 1884 p. 146—168) 
have had but little influence. Thus, in 1887, Riprey & Dernpy divide 
the spicula of the Monaxonids in the first place into Megasclera and 
Microsclera, a classification which practically agrees with those of 
BoweRBANK and CARTER. The example was followed by Sorras in 
spite of his being well aware of the fact that the distinction is far 
from “absolute”. This author quite correctly remarks (1888, p. LIID): the 
microscleres and megascleres pass into each other by easy gradations, 
so that it is not possible to say where one ends and the other begins, 
indeed there would be a certain convenience in accepting a third 
division of intermediate or middle-sized spicules, which we might call 
mesoscleres.” Finally, in 1889, Scuunze & LENDENFELD accept SCHMIDT’S 
primary division into “polyaxone, tetraxone, triaxone, and monaxone 
Nadeln.” 
I do not intend to discuss here the triaxons and tetraxons; for 
the present I only wish to draw attention to some monaxons and 
some spicules hitherto generally considered as polyaxons. 
In the group of the monaxons, i.e. spicula with one single axis, 
two fundamental divisions may be distinguished, according to the 
