598 
MR. HUXLEY ON DOLIOLUM AND APPENDICULARIA. 
saw “living animals” proceed from it, the part being afterwards evidently col- 
lapsed. 
Unfortunately, however, he does not appear to have noticed the endostyle, whence 
confusion might readily arise ; nor does he give the slightest hint as to the nature of 
the “living animals ” which he saw come forth. 
85. Still less am I able to give any explanation of the extraordinary envelope or 
“ House ” to which, according to Mertens, each Appeiidicidaria is attached in its 
normal condition. I have seen many hundred specimens of this animal, and have 
never observed any trace of this structure ; and I have had them in vessels for some 
hours, but this organ has never been developed, although Mertens assures us that it 
is frequently re-formed, after being lost, in half an hour. 
At the same time it is quite impossible to imagine, that an account so elaborate and 
detailed, can be otherwise than fundamentally true, and therefore, as Mertens’ paper 
is not very accessible, I will add his account of the matter., trusting that further 
researches may clear up the point. 
The formation of the envelope or “Haus” commences by the development of a 
lamina from the “ semicylindrical organ” (ganglion?). This, as it grows, protrudes 
through the opening at the apex of the animal (respiratory aperture). Its corners then 
become bent backwards and inwards, and thus a sort of horn is formed on each 
side, the small end of which is turned towards the apex of the animal, while its 
mouth looks backwards, downwards and outwards. 
At the same time two other horns are developed upwards (the animal is supposed 
to have its small end downwards), one on each side. These are smaller and more 
convoluted than the others. 
This four-horned structure consists of a very regular network of vessels, in which, 
at the time of the development of the organ, a very evident circulation is visible ; the 
blood-corpuscles streaming from the attached end of the organ. “ The clearness with 
which the circulation was percej)tible, together with the great abundance of vessels 
and the large extent over which they were spread, were circumstances which led me 
(says Mertens) to believe this truly enigmatical structure to be an organ, whose 
function was the decarbonization of the blood. The ease with which the animal 
becomes separated from this organ is no objection to this view ; the necessity there 
seems to exist for the reproduction of the latter rather confirming my opinion.” 
It is highly desirable that more information should be gained about this extraordi- 
nary respiratory organ, which, if it exist, will not only be quite sui generis in its class, 
but in all animated nature. And in a physiological point of view, the development 
of a vascular network, many times larger than the animal from which it proceeds, in 
the course of half an hour, will be a fact equally unique and startling. 
86. As to the zoological relations of Appendicularia, its discoverer, as we have seen, 
considers that “it may possibly be allied to Cestum,' a conjecture in which no one 
can possibly coincide. 
