TUNICATA. 321 



examined had alone beeii found, or even if the first and second only had been known, 

 the species might have been described as destitute of branchial sac, stomach, and 

 intestine. And yet the third example, which there is no reason to think belongs to a 

 different species, shows a perfectly normal structure. I have no doubt that specimens 

 one and two have lost their alimentary tract. From WILLEY'S observations it seems 

 possible for an Ascidian by a powerful contraction of the mantle under some abnormal 

 conditions to perform evisceration and get rid of the entire free portion of the canal, 

 from the peripharyngeal bands to the anus, and that seems to be the best explanation 

 of all such abranchiate specimens. 



The tentacles remain, as they are firmly attached to the muscular body- wall, and 

 they are alike in all the three Ceylon specimens. Fig. 39 shows the appearance of a 

 stained preparation of a tentacle, where (a) indicates a band of ciliated columnar 

 epithelium, the rest of the surface being covered with squamous cells, while (b) is a 

 tract of solid connective tissue, along the convex edge, which stains a bright red with 

 picro-carmine, and is probably skeletal in function. The rest of the interior contains 

 lacunae with many blood corpuscles (c). 



The only difference that is apparent between the normal and the abranchiate 

 specimens is that the latter have a more abundant crop of endocarps projecting from 

 the body-wall (fig. 36), and as these are individually larger (figs. 40 to 42) and 

 contain lacunae in connection with those of the mantle outside (fig. 36), and show 

 many blood corpuscles in their interior, I would suggest that this greater development 

 of these thin-walled vascular processes has taken place in order to compensate for the 

 absence of the branchial sac by promoting respiration. SLUITER, in his original 

 mutilated specimen, Styela abranchiata, found that the mantle was thickened and 

 highly vascular, and he recognised that its condition compensated for the absence of 

 the normal respiratory organ. In Styela solvens, however, no unusual development 

 of the mantle is described. Whether any nutrition can be effected by amoeboid cells 

 in the body-wall absorbing particles brought into the single large cavity by the 

 branchial and atrial apertures, and whether the animal can maintain life for long in 

 this abnormal state, there is no evidence to show. Experimental work on eviscerated 

 specimens would be necessary to determine such points. 



If the animal is able to carry on existence in this mutilated condition, two 

 physiological points arise : the one as to respiration and the circulation of the blood, 

 the other as to digestion and nutrition. The heart and the chief blood-vessels have 

 gone with the other loose viscera. The abundant thin- walled endocarps containing 

 blood lacunas and projecting freely into the sea- water in the peribranchial cavity no 

 doubt perform respiration effectively, and it is possible that they pulsate like the 

 ampullae in the test of Botryllus and so keep the blood in movement. The other 

 possibility is that contraction of the muscles in the mantle squeezes the blood 

 irregularly from place to place in the body-wall and so prevents stagnation. 



In regard to nutrition, it seems possible that amoeboid cells in the connective-tissue 



2 T 



