MR. HUXLEY ON DOLIOLUM AND APPENDICULARIA. 
601 
which are turned inwards. The base of the tube is surrounded by a thickened mus- 
cular rim. 
The posterior extremity is similarly produced into a short tube with a thickened 
base, but the tube looks outwards, and its walls are very delicate, and consist of fine 
fibres like those of the fin of Sagitta. 
90. The body of the animal consists of two tunics, an inner and an outer*, which 
surround a wide central respiratory cavity. 
Six muscular bands {t), pretty nearly equidistant, gird the inner tunic. 
In some specimens a sort of shrivelled tubular process projects on the dorsal 
surface posteriorly between the two last muscular bands. Is this the remains of an 
earlier pedicle of attachment ? 
91. A tubular endostyle (c) lies in the dorsal sinus between the first and third 
muscular bands. 
In the ventral sinus a round ganglion {a) lies just in front of the third muscular 
band. It gives off several long nerves, four of which are especially remarkable, and 
run diagonally to the anterior and posterior apertures. There is no auditory sac nor 
otolithes. 
92. The branchiae divide the respiratory cavity into an anterior and a posterior 
chamber. They are formed by the epipharyngeal and hypopharyngeal {x) bands which 
stretch aross the respiratory cavity, supporting on each side a number of tubular 
bars {y). In the upper and lower division of the branchiae, these bars are adherent 
to the walls of the respiratory cavity, i. e. to the inner tunic, and there their canals 
open into the lateral sinuses ; but in the middle part of the branchiae their extremi- 
ties unite and form loops without adhering to the inner tunic, merely lying against 
it. There is a free passage for the water between the bars, and on each side of the 
central supporting bands. 
The edges of the bars are richly ciliated, and the cilia of their opposite sides move 
in opposite directions. 
Although it appeared quite certain that the canals of the bars communicated with 
the sinus system, yet no blood-corpuscles could be traced into them. 
The branchial bars did not extend so far forward above as below. In the former 
case they reach as far as the second muscular band only, in the latter, beyond the 
first ; seen from above or below, the branchia appeared as an oval plate, with a clear 
space down its middle and transverse bars on each side. 
93. The mouth (g) opens in the middle of the upper division of the gill, just anterior 
to the fourth muscular band ; a narrow oesophagus (h) leads from it into a two-lobed 
stomach (i) ; from this a narrow intestine passes, and bending a little upwards and 
then downwards and to the left side, terminates in a papillary (/) anus. Just at its bend 
* The outer tunic, which I consider as homologous with the test and outer tunic of the Ascidian fused 
together, was found by MM. Lowig and Kolliker to contain cellulose, whence they concluded the Ascidian 
nature of the animal, a deduction strikingly confirmed by anatomical investigation. 
