THE GENUS APPENDICULARIA. | 301 
Atlantic, near the Line, and occasionally as far north as off the coast of Portugal. It can 
be distinguished at first glance from any of its Appendiculate brethren by the peculiar 
‘seroll-like manner in which its slender lanceolate flabellum is rolled upon itself when the 
animal is at rest. 
When examined under a magnifying-power of about 100 diameters, the internal eco- 
nomy of this form is seen to differ widely, as regards its respiratory arrangements, from 
any of the known species. The oval half of the globular body contains a large branchial 
sac, with a ganglion and otolithe in the usual positions in its anterior paries, but with 
its posterior lining-membrane folded into a gill-like structure (fig. 5, v), wide in the 
centre and tapering to either end, extending from the posterior lip of the branchial orifice 
to a point close to the insertion of the appendix, and presenting a double series of narrow 
trausverse slits, which give the whole structure a general resemblance to the respiratory 
diaphragm of Doliolum, though on a lengthened and much more minute scale. "The last 
eurve of the intestine lies transversely across the centre of the body, above a globular 
ovary, and terminates on the right side in a papilla, through which the rectum opens. 
. The main nervous trunk, descending from the ganglion, curving round the stomach, 
and entering the appendix, presents no distinctive peculiarities. 
In many specimens of Appendicularia, pear-shaped organisms have been found, attached 
by slender stems to various parts of the outer tunic, so like the pallio-vascular stolons of 
Compound Tunicaries as to suggest the existence of an ascidarium at some developmental 
stage, and that possibly the ** enigmatical * Haus’ of Mertens " might be in some way con- 
nected with such an ascidarium ; but further observation has convinced me that these 
pseudo-stolons, as well as an irregularly papillated condition of the outer coat sometimes - 
met with, are merely parasitic growths, and that the ** Haus” is an exfoliation of the tunics 
connected with a yet unknown vital process. Both groups of Appendiculariæ possess 
the power of forming the “ Haus ;” but that evolved by the long-bodied is small and so 
extremely delicate as only to be seen under the most favourable conditions. The fol- 
lowing notes have therefore been principally gleaned from observations of the behaviour 
of members of the short-bodied group. 
When the animal is about to form a‘ Haus,” its rapid jerking movements cease, and 
after about a minute’s rest, a transparent membrane is seen to project beyond the outline 
of the tunic over the upper part of the body ; it soon after flexes its appendix until the 
tip touches the newly evolved structure, then, slowly extending it, draws the gossamer- 
like membranes completely over both body and appendix. If, however, the animal is 
disturbed during the process of evolution, it at once shakes itself free, and the structural 
details of the immature formation thus obtained are more distinct and compact than 
when fully extended; the annexed illustration (fig. 7) has therefore been sketched from a 
** Haus ” thrown off when the tenant had just commenced to incurve its appendix. The 
general shape of the fully formed ** Haus ” may perhaps be described by comparing it to 
a thick-winged butterfly, the little Tunicate swimming, branchial orifice upwards, between 
the viscid alæ, and slowly propelling the whole mass by the undulations of its iridescent 
- flabellum, which projects backwards between the wings. Even in a large aquarium the 
- little animal seldom remains more than an hour in the “ Haus;" a second one, as Mer- 
