582 
MR. HUXLEY ON THE ANATOMY OF SALPA AND PYROSOMA. 
The intestine (r, s, t) commences by a wide mouth with thick lips, at the posterior, 
ventral extremity of the respiratory cavity. The oesophagus (r) runs back, and then 
upwards to terminate in the wide subquadrilateral stomach (t). A narrow pylorus 
communicates with the intestine, which passes at first upwards and forwards, and 
then suddenly becoming bent upon itself, runs downwards and to the right side, to 
end in the wide flattened anus (r). 
The oesophagus is dotted over with branched carmine pigment-cells ; and similar 
cells are frequently seen upon the intestine just beyond the pylorus. 
47. A tubular axis (u) arises from the stomach, and branches out on the rectum 
into a system of tubes as in Salpa ; but the ramifications are less numerous and less 
regular, with v/ider meshes than in the latter. The tubes are less transparent and 
have more the appearance of solid fibres, and finally they terminate towards the anus 
in wide globular caeca. 
The stem of this system is about j^Voth of an inch in diameter, 
48. Each zooid is composed of two tunics, an outer (a), confluent with the general 
cartilaginous basis, and an inner ((3), continuous with the outer at its anterior and 
posterior extremities, and adherent to it antero-laterally, in two oval spots, one on 
each side, which, when examined by the microscope, appeared to consist of nothing 
more than an aggregation of clear circular cells about -g-^th of an inch in diameter. 
(5). These were considered by Savigny to be the ovaria, but they have not the ap- 
propriate structure, and it will be seen that the ova are formed elsewhere. 
In all the rest of their extent the inner and outer tunics are separated by a very 
obvious space. This is one large vascular sinus, and the viscera lie in it and are 
bathed by the blood which fills it. 
The heart (^) is placed on the dorsal side just behind the posterior extremity of the 
internal shell. In structure it perfectly resembles that of Salpa, and its contractions 
are reversed in a similar manner. No distinct vessels were to be traced in these 
animals. 
49. The endostyle (c) resembles that of Salpa in its structure. It is as long as the 
branchial chamber, and lies in the dorsal sinus, supported by a projeeting ridge of 
the inner tunic. On each side of it below, there is a longitudinal thickening, which 
readily gives rise to the appearance of four dorsal bands or ‘‘^undulated vessels,” 
described by Savigny. 
50. The branchiae {v) are symmetrical, one on each side, and are composed of a 
network formed by longitudinal and vertical bars or laminae. 
The vertical bars are outside ; the longitudinal bars are at equal distances along 
their inner surface, and are attached at the point of intersection. 
The vertical bars are attached to the inner tunic at their upper and lower extremi- 
ties ; for the rest of their extent they are free. 
The longitudinal bars {v, fig. 3) are rather larninse, flattened horizontally, 
slightly thickened at their free edges, and beset along the upper surface of these 
