AND DEVELOPMENT OF PYROSOMA. 
201 
tendent of the Marine Department of the Board of Trade, kindly forwarded to me a wry 
beautiful specimen of Pyrosoma giganteum, taken by Captain Callow* in the North 
Atlantic, about 400 miles S. of the Cape De Verd Islands, in the month of August of that 
year, and admirably preserved by immersion in strong spirits. I was aware, from former 
experience, that the textures of Ascidians, in general, are admirably conserved in spirit- 
specimens which are even many years old; and I therefore commenced my inquiries 
with a sanguine expectation of being able to make out something about the origin of 
the compound embryos, which a cursory inspection of the specimen proved to exist in 
abundance. I must confess, however, that I had no anticipation that researches con- 
ducted upon a preserved specimen of any animal could be followed out so far as I have 
been led, step by step, to carry these. And had I not had the opportunity of showing 
many of my preparations to observers of experience and authority, who can b<ar witness, 
at any rate, to the perfect distinctness of the most important of the appearances described, 
I should hardly have hoped to secure a patient reception for delicate embryologie.il 
inquiries which profess to have been conducted upon thin sections of a* spirit-speciinen, 
rendered clear by glycerine. 
I have already published a brief notice of the most important tacts 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. 
l 
§ 2. The Anatomy of Pirosoma giganteum. 
In the specimen of Pyrosoma under description, the ascidiariumf 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 Jth 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 
haemal, inasmuch as the heart is situated on that side of the body of «\cry 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 ascidi rium is it- 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 pro- 
cesses and varying in elevation, until they hardly project at all above the general level of 
the convex surface of the ascidiarium. Each of these eminences hears a small rounded 
Finding a specimen could be procured in no other way, this gallant and skilful seaman swam for that he 
obtained. He informs me that it emitted a strong bluish-white light, sufficient to read small print by. 
t The entire body of a compound Ascidian may be conveniently termed the ascidiarium, while the separate 
zooids may be called ascidiozooids. 
VOL. XXIII. 
2 E 
