REPORT ON THE TTJNTCATA. 93 



Tlie Test is moderately thick and strong, but quite soft and flexible Its outer 

 surface is rough on account of the presence of small processes scattered thickly all over, 

 and developed in certain places into papilla-like tufts. These processes are of a brownish 

 colour, while the test at their base has a slightly grey tint ; where the processes are few or 

 of small size this slate colour shows, elsewhere the general appearance is brown. The 

 test is quite opaque. 



On the inner surface, when the adhering mantle has been removed, the test has a pale 

 hyaline blue tint, with minute dots or punctures all over it. Under a low power of the 

 microscope (50 diameters) this appearance is seen to be caused by the presence of a large 

 number of small chambers deeply imbedded in the test (as viewed from the inner surface). 

 These are all very nearly of the same size, and are so numerous that the bars left between 

 them seem to mark out the entire surface into polygonal areas. Most of these chambers 

 in this view are seen to be occupied by masses of reddish-brown blood-corpuscles. 



In thin sections through the test the minute papillae on the outer surface are seen to 

 be hollow (PI. VIII. fig. 2, t.p.), and their large bases contain the chambers seen from the 

 inner surface. These chambers or interior spaces of the papillae extend, however, a little 

 into the thickness of the test ; they are in direct connection with the blood-vessels 

 ramifying through the substance of the test, and frequently in sections one of the 

 terminal twigs of the vessels is seen entering the base of a chamber (PI. VIII. fig. 

 2, t.k.'). The vessels in this test seem rather feebly developed. They are not present in 

 large numbers in any of the sections, and they are of small size. These chambers 

 occupying the papillae seem to be a modification of the knobs on the ends of the terminal 

 twigs of the vessels so well developed in many species of the genus Ascidia, and like 

 them are generally filled with blood-corpuscles. Lacaze-Duthiers states 1 that the hairs on 

 the test in the Molgulidas are merely the terminal knobs greatly developed in length. 

 In the present case we have them extending beyond the surface of the test as a series of 

 hernia-like papilla). The larger projections, however, found round the branchial and 

 atrial apertures, and on the belt round the posterior end, are comparable with the hairs 

 of the Molgulidtu, although their function appears to be different, as I have never 

 observed any foreign matter adhering to these processes. They are conical in shape, 

 taper to a blunt point, and have usually a considerable number of short lateral 

 branches which frequently bifurcate at the tip, and in some cases end in a clump com- 

 posed of several little papillae (PI. IX. fig. 3, t.k/). The whole process is hollow and 

 very thin-walled. It is, like the chambers at the bases of the smaller papillae, 

 directly continuous with the blood-vessels of the test, and usually contains blood- 

 corpuscles. 



It is difficult to say what the use of these processes of the test can lie. Their 

 connection with the vascular system and their thin walls suggest a respiratory function, 

 1 Archives de Zoologie exp^rinnntak' et gi m rale, vol. iii. p. 314 (1874). 



