Hi 
THE VOYAGE OF H.M.S. CHALLENGER. 
directness of expression which is gained by the use of a new word when it sums up in 
itself a whole phrase. This perhaps may explain the fact that those who chiefly cavil at 
new terms are our ancient friends the phrasemongers. 
The distinction between essential and auxiliary skeletal spicules (Bowerbank), or 
skeletal and flesh spicules (Carter), is of great convenience, and we shall adopt it here, 
terming the skeletal spicules megascleres, and the flesh spicules microscleres ; it is easy, 
however, to fall into the mistake of regarding this distinction as absolute, while truly it 
is a mere matter of relative size ; 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; thus in Pcecillastra {Normania)^ 
there are found megascleres which form the chief framework of the sponge, microscleres 
which are strewn through it separately, seldom near enough to be in actual contact, and 
finally mesoscleres which lie close together, forming a dense felt; if these last-named 
spicules occurred alone as similar spicules do in Halichondria jpanicea, they would almost 
certainly be classed as megascleres, indeed Carter, in describing similar cases, does not 
hesitate to call them skeletal, but in Pmcillastra and similar cases they would be classed 
as flesh spicules, and in the descriptive part of this Eeport they will be found under the 
head of microscleres. Although the use of the term mesosclere has thus much to 
recommend it, I have not yet adopted it, since it was not discussed at our conference in 
London, and it is just one of those points which require discussion by the workers in 
different groups ; it is to be hoped, however, that a general conference of spongologists 
may be held at some future date, when the whole subject of spicule nomenclature may 
be fully considered, and a universal system adopted. 
In describing the various forms of spicules we shall commence with the megascleres : — 
Class I. Megascleres (Megasclera, aK\r}p6<s, d, 6v, hard). 
Comparatively large or “ skeletal ” spicules. 
The megascleres are divided into the following groups, according to the number and 
distribution of their axes. 
Group 1. Monaxons (Monaxona). 
Megascleres of a rod-like form, in which growth is directed from a single origin in one 
or both directions along a single axis. The ray or rays of a monaxon are known as an 
actine or actines. 
The axis of the monaxon as of other megascleres is not necessarily straight, it may be 
curved or undulating. 
