66 TUNICATA——APPENDICULARIANS CHAP. 
Mertens, and by him named “ Haus”; it has recently been more 
minutely investigated by Lohmann. It is only loosely attached 
to the body, and is frequently thrown off soon after its formation. 
Its function is probably protective, and possibly to some extent 
hydrostatic, and it may also be of use in straining the nutritive 
particles from the large volumes of water which filter through its 
complicated passages and perforated folds. The long, laterally 
compressed “tail” in the Appendiculariida is attached to the 
ventral surface of the body (Fig. 30), and is bent downwards and 
forwards, so that it usually points more or less anteriorly ; and is 
twisted through an angle of 90°, so that the dorsal edge les to 
Fic. 28.—Appendiculariida. A, Appendicularia sicula, Fol, with house ; B, Megalo- 
cercus abyssorum, Chun, nat. size; C, Oikoplewra cophocerca, Gegenb., with house ; 
D, Fritillaria megachile, Fol, with vesicle; E, Appendicularian in its house ; 
F and G, two stages in the formation of the house. (A toD from Seeliger; E to G 
from Lohmann.) 
the left. It shows what have been interpreted as traces of meta- 
meric segmentation, having its lateral muscle-bands broken up 
into successive pieces (supposed myotomes, probably only cells), 
while the nerve-cord presents a series of enlargements formed of 
groups of nerve-cells from which distributory nerves are given off. 
In Oikopleura the muscle-band in the tail is formed of ten cells 
fused on each side. Near the base of the tail there is a distinctly 
larger elongated ganglion. The urochord in the tail consists of 
a homogeneous rod surrounded by a sheath containing nuclei. 
The anterior (cerebral) ganglion has connected with it an 
otocyst (Fig. 29), a pigment spot, and a tubular richly ciliated 
process opening into the branchial sac, and representing the dorsal 
tubercle and associated parts of an ordinary Ascidian. The tube 
ends in a plain or coiled cellular mass lying to the right of the 
1 See Lohmann, Schrift. Naturw. Ver. Schlesw.-Holst. xi. 1899, 347. 
