324 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
logical inquiries which profess to have been conducted upon thin 
sections of a spirit-specimen, rendered clear by glycerine. 
I have already published a brief notice of the most important 
facts which have been developed by my investigations in a paper 
published in the ‘ Annals of Natural History’ for January 1860, and 
in a communication to Section D. of the Meeting of the British 
Association at Oxford in July 1860. 
§ 2. The dnatomy of PYROSOMA GIGANTEUM. 
In the specimen of yrosoma under description, the ascidiarium ! 
is a firm, hollow, conical body, 4 inches long, and about ths 
of an inch wide at its broad, open end, whilst its rounded apex 
measures hardly more than half an inch. The translucent, colourless 
wall of the ascidiarium is on an average about ;';ths of an inch thick ; 
but it thins towards the open end, ending in a sharp ledge or rim, 
which is bent horizontally inwards and ends in a sort of circular 
valve-like lip, nearly th of an inch wide, around the aperture of the 
central hollow or cloaca. 
In relation to the ascidiozooids, the closed, apical, end of the 
-ascidiarium is dorsal or hemal, inasmuch as the heart is situated on 
that side of the body of every ascidiozooid which is turned towards the 
apex. The nervous ganglion, on the other hand, is on the opposite 
side of the body, so that the open extremity of the ascidiarium is its 
neural end. 
The outer surface of the ascidiarium is rendered uneven by conical 
-eminences, which are scattered over it at irregular intervals, and which 
are elongated on their neural sides into longer or shorter processes. 
Among these lie similar eminences without such processes and 
varying in elevation, until they hardly project at all above the general 
level of the convex surface of the ascidiarium. [ach of these eminences 
bears a small rounded aperture, the oral opening of an ascidiozooid ; 
and there are other, similar, apertures, dispersed between the 
eminences. In the specimen under description, the ascidiozooids are 
almost colourless, or have at most a very pale brownish hue; but 
how much of this colourlessness may be due to the action of the 
spirit, I do not know. 
Such is the general appearance of the ascidiarium. To examine 
its internal structure, it is expedient to make sections with a razor in 
1 The entire body of a compound Ascidian may be conveniently termed the ascédarzum, 
while the separate zooids may be called asczdvozoods. 
