REPORT ON THE TETRACTINELLIDA. 
clxi 
in the Tetillidse is reduced to a disene and even a monsene, a fact which on the 
assumption that the trisene is derived from a calthrops, would lead us to regard it here 
as a waning form. 
If next the weight of evidence should lead us to abandon the assumption just made 
as to the origin of the trisene and to regard it as descended from a rhabdus, and the 
sigmaspire from a euaster, then we might construct our phylogeny on the assumption of 
a hypothetical ancestral family (Pansigmata) in which the skeleton should have consisted 
wholly of sigmaspires from which rhabdi on the one hand and microtriods and micro- 
calthrops on the other would have been derived ; we should then have the following : — 
Astropliora 
Sigmatopliora Spintharopliora 
Meniscopliora Microsclerophora 
Pansigmata 
The obvious objection to this scheme is the wide separation it involves betvv^een the 
Microsclerophora and the Astrophora, which we have good reason for believing to be 
more directly related ; and in so far as it is thus rendered improbable, it throws doubts 
on the assumption on which it is based, i.e., the rhabdal origin of the trisene. On this 
vexed question it would thus appear that Taxonomy and Ontogeny offer conflicting 
evidence, but considering how scanty the evidence is, particularly that furnished by 
Ontogeny, this is no wonder, and with an extension of knowledge a speedy reconcilia- 
tion is certain. 
7. METHODS OF INVESTIGATION. 
Preliminary Examination . — The gross anatomy of the Sponge, including the general 
characters of the ectosome or cortex, of the canal-system, and the forms and disposition 
of the spicules, is most conveniently investigated by means of thick slices cut free-hand 
with a razor ; these are stained with any rapidly acting dye-stuff,- — magenta answers as 
well as any, — dehydrated with absolute alcohol, cleared with xylol in the usual way, and 
finally mounted in Canada balsam. By this process, which does not take longer than 
from five to ten minutes, the generic and usually the specific characters also of nearly all 
Tetractinellid Sponges can be determined. The flagellated chambers and other minute 
structures are frequently displayed by this process in the case of such Sponges as possess 
(ZOOL. CHALL. EXP. PART LXIII. 1888 .) RlT X 
