152 MR. C. DARWIN ON THREE SEXUAL FORMS 
A. deep chamber, which from its homological relations must be 
ealled the stigmatie chamber, lies between the bases of the an- 
Fig. 1. 
l 
CATASETUM TRIDENTATUM. 
a. anther. ~ an. antennæ. 
pd. pedicel of pollinium. l labellum. 
A. Side view of flower in its natural position with the properly lower sepals 
cut off. 
B. Front view of column, placed upright. 
tenne ; and the anther, with its concealed pollen-masses, is seated 
above. My object is not here to describe in detail the structure 
of the flower and its curious mechanism. But it must be observed 
that the ovarium is much shorter, thinner, less deeply furrowed, 
more solid in the centre, and the bract at its base smaller, than 
in the two sueceeding sexual forms presently to be described. 
The ovarium is bent so that the bucket-like labellum stands upper- 
most, instead of forming the lower lip as in most Orchids 
From what I had myself observed previously to reading Sir R. 
Schomburgk's paper, I was led to examine carefully the female 
organs of this species, and, I may add, of C. callosum and C. sacca- 
twn. In no case was the stigmatic surface viscid, as it is in all 
other Orchids (excepting Cypripediwm), and as is indispensable 
for securing the pollen-masses on the rupture of the caudicles. 
I carefully looked to this point in both young and old flowers of 
C. tridentatum. When the surface of the stigmatic chamber and 
of the stigmatic canal of the above-named three species is scraped 
off, after having been kept in spirits of wine, it is found to be com- 
posed of utriculi (with nuclei of the proper shape), but not nearly 
so numerous as with ordinary Orchids. The utriculi cohere more 
together, and are more transparent. I examined for comparison 
the utriculi of many kinds of Orchids, which had been kept !! 
