402 Mr. J. D. Macdonald on a new form of Compound Tunicata. 



system of tubes, which exhibit in general a longitudinal arrange- 

 ment in the tissue of the stem (PI. XI. fig. 2 q), and give rise to 

 numerous sacculations spreading peripherically. When this tubu- 

 lar prolongation is cut across, the test may be easily peeled off, 

 as it were, leaving the animal in a fit state for examination. 



The external apertures close up in four irregularly puckered 

 folds, but do not exhibit much prominence. 



The branchial orifice, which opens upon the upper surface 

 about one-third from the extremity, is furnished internally with 

 a dense circlet of simple subulate tentacula (fig. 6 e), whose bases 

 are continuous, on the one hand, with the epithelial membrane 

 of the branchial sac, and, on the other, with that which invests 

 the muscu.lar coat and the viscera, and terminates in the tubular 

 process of the pedicle above noticed. 



The muscular tunic is composed of an open work of delicate 

 fibres disposed in diff'erent directions, but chietiy running trans- 

 versely, and the short cylindrical tubes of the external openings 

 are furnished with circular and radiating bundles strongly re- 

 sembling those of Boltenia. 



The mouth (PI. XI. fig. 2/) is sitiiated near the centre of the 

 inferior wall of the respiratory chamber, leading rather suddenly 

 into a lengthy cesophagus {g), which, after having reached the 

 extremity of the thorax, opens into a subglobular stomach (A) 

 with thick glandular walls tinted with a reddish-brown pigment. 

 This viscus tapers off internally, to form a kind of duodenum 

 coated with amber-coloured cells, which probably fulfil the office 

 of liver. 



The intestine here curves upon itself dextrally, and the rectum 

 may be said to course the whole length of the body and termi- 

 nate close to the cloacal outlet. 



A distinct ovarium (m) and testis (o) are packed together in 

 the loop of intestine, and the delicate vas deferens and a wide 

 oviduct pass outwards side by side between the cesophagus and 

 rectum towards the cloaca. 



Ova in the immature state may be seen in the ovarium, crop- 

 ping out below the duodenum ; but a cluster of several, contain- 

 ing tadpole-like embryos in different stages of development, 

 usually occurs in a sacculus of the duct (w) below the oesophagus ; 

 while others, still further advanced, appear to lie loosely in the 

 branchial sac, quite unconnected with the cloaca. 



The heart (/), occupying a distinct pericardium, lies imme- 

 diately above the intestinal loop ; and holding a longitudinal 

 position, its alternately reversed vermicular contractions may be 

 easily observed during life. 



A well-marked endostyle {d) is traceable along the upper or 

 dorsal wall of the respiratory chamber, from the inner side of 



