352 ARANEIDEA. 
specialized as we now know it, is a very ancient organ, antedating, not only in its 
origin, but in its actual functional specialization, the division of the Aranez into the 
various broad families at present recognized. If we hold this view, we may regard all 
the spiders in which the cribellum is now specialized as the offshoots of some one or 
more ancestral forms, divergent in this particular respect from the main body in which 
no specialized cribellum was developed. The pair of rudimentary abdominal appendages 
whence the cribellum was developed would of course have been possessed by all forms 
without exception. All subsequent divergence of the eribellate forms into widely 
differing genera or groups, such as Hypochilus, Filistata, Ccobius, Uloborus, Zorocrates, 
Psechrus, Amaurobius, &c., would therefore be due to subsequent environmental action . 
and reaction. 
We should have to explain, too, the extraordinary structural resemblances between, 
for instance, Acanthoctenus (cribellate) and Acantheis (non-cribellate) ; Psechrus and 
Tegenaria; Amaurobius and Celotes ; Zoropsis, Zorocrates, and the Drassids, cribellate 
and non-cribellate forms respectively; and many others, as cases of coincidental convergent 
development, under similar conditions, of two distinct branches of spider-forms, long 
ago widely divergent, reapproaching each other in the present plane of existence owing 
to passage through similar environmental influences. 
If this theory be accepted, with the assumptions necessary to its consistency, then 
we shall, as Simon has done, divide the Aranez into “‘ Cribellate ” and “ Kcribellate.” 
But if not, there is an alternative theory (2), that the cribellum is a comparatively 
recent specialization of the anterior surviving pair of abdominal appendages possessed 
originally by all early forms, at any rate long post-dating the conditions under which 
the divergence into the present groups was initiated. 
If we accept this view, we shall have no difficulty in accounting for the extraordinary 
resemblances noted above, and we shall find our conclusion more in accordance with 
the evidence at present available, furnished by the cribelium, the intermediate organ, 
and the vestigial colulus. | 
One must admit, however, that in this case we shall have a similar difficulty in 
explaining how these rudimentary appendages should acquire a specialization so very 
similar in character in such widely divergent groups as are represented by Hypochilus, 
Filistata, Deinopis, &c., especially when correlated with another organ, the calamistrum, 
situated on almost exactly the same portion of the same segment of the posterior 
legs. In all probability, however, the abdominal appendages (which remain in full 
evidence in Liphistius) were amongst all ancestral forms more or less adapted, in 
connection with internal glands, for secreting and exuding silk; and, in certain cases, 
circumstances favoured the correlative specialization of the cribellum in connection 
with the calamistrum, and the latter in the exact position we find it, because this 
happens to be the only position in which hairs (becoming a row of specialized 
bristles) could be swept across the organ and facilitate the dispersal of the silk, 
