166 THE VOYAGE OF H.M.S. CHALLENGER. 



tudinal bars arc very strong. The meshes intermediate to the slighter folds are large 

 and square, and are not subdivided by any smaller vessels. 



The Dorsal Lamina is a broad plain membrane, slightly undulating at the free edge. 



The Tentacles are large and simple, from twenty to twenty-five in number, and all of 

 one size 



The Dorsal Tubercle is small and simple, nearly circular in outline, and has the aperture 

 anterior and rather wide. The horns are not coiled. 



The Alimentary Canal is situated on the left side, near the dorsal edge. 



The Genitalia are two elongated glands — one on each side. 



This remarkable form is closely allied to Styela, from which it is separated generically 

 on account of the peculiar branchial sac, which exhibits the simple structure only known 

 in the two allied genera Culeolus and Fungulus. 



In external appearance (PI. XXIV. fig. 8) it is small and rudely ovate, with the pos- 

 terior end narrow and roughened. On account of the thin and transparent test it looks 

 rather like a Molgnla. The mantle has a large number of muscle bands, forming a minute 

 network, but they are very delicate. The branchial sac (PL XXIV. fig. 9) is, however, 

 undoubtedly the most remarkable feature. It is formed of two series of vessels — the 

 transverse and the internal longitudinal — intersecting at right angles. The internal 

 longitudinal bars are placed in threes, and each set (forming one of the slighter folds or 

 projections) is held together by a double series of short transverse vessels, smaller inter- 

 mediate ones being placed between those which extend all round the sac. In other words, the 

 smaller alternate transverse vessels are confined to the folds. The meshes between the folds 

 (PI. XXIV. fig. 9) are large and square. As no fine longitudinal vessels are present, there 

 are no true stigmata. On the left side of the branchial sac, near the dorsal lamina, there is 

 a collection of about six or eight internal longitudinal bars, forming a much larger fold. 



The tentacles (PL XXIV fig. 10) are simple and stout. They are not long, are all of 

 one size, and are pretty closely placed. The anterior face of each is a flattened plain 

 surface while the posterior or branchial is highly arched and somewhat irregular, the 

 membrane being loose and puffed out in parts as in most Molgulidee. 



The dorsal tubercle (PL XXIV. fig. 11) is rather simple, and is placed at the anterior 

 extremity of the funnel-shaped tube leading to the neural gland. The peritubercular area 

 is not large, and has an irregularly triangular form. The nerve ganglion is large and 

 oblong in shape. It gives off a considerable number of nerves at each extremity. Its 

 anterior (branchial) end is just at the posterior angle of the peritubercular area. 



The intestine is of much the same cabbre throughout its length. It is rather small, 

 and lies near the dorsal edge of the left side. 



The genital glands are in the form of elongated undulating bodies attached to the 

 inner surface of the mantle, one on each side, and converging towards the atrial aperture. 



