958 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The dorsal raphe in the genus Cynthia, as in Ciona and Phopalona, 

 is formed of a series of delicate languettes, and a dorsal groove is 

 present ; but in the genera Microcosmus, Styela, and Polycarpa this 

 groovo is absent, and the raphe is formed of a membrano as in most 

 of the Phallusiadro. 



The form of the " posterior raphe," which is always in part dorsal 

 in position, varies in the different genera. 



The alimentary tract is placed on the left side of the animal, as 

 in the genus Ascidia, and is united to the dermis either directly, or, in 

 Polycarpa, by means of membrane. 



The entrance to the oesophagus from the pharynx (branchia) is 

 surrounded by a smooth " oesophageal area," which varies charac- 

 teristically in different genera ; the dorsal raphe passes along the left 

 side of the area ; the posterior raphe comes up to meet it ; the wall 

 of the oesophagus is traversed by four or five deep furrows. The 

 wall of the stomach is similarly thrown into numerous folds, as in 

 the Phallusiadse. Microcosmus is exceptional, in that the alimentary 

 tract, with the exception of the rectum, is embedded in the large 

 genital gland. 



The structure of the stomach in the various genera is given in 

 detail, both macroscopically and histologically. The cells which line 

 the grooves contain numerous yellowish-green granules, probably 

 indicating a biliary secretion. 



The intestine has a lining of cylindrical epithelium containing 

 goblet-shaped mucous cells. This is surrounded by the epithelium 

 (ectoderm) of the peribranchial cavity, as is also the stomach. There 

 is a typhlosole in Styela and Polycarpa. 



The nervous system resembles that found in Ascidians generally. 

 There is no large coelom in the adult simple Ascidians, though 

 present in the larva. The in-pushed peribranchial cavity obliterates 

 it, the outer wall of which becomes pushed against the body-wall, 

 and the inner wall against the intestinal and branchial wall. How- 

 ever, the pericardium and the cavity in which the renal and genital 

 organs lie, are representatives and remnants of the once more 

 extensive coelom. 



The circulatory system, as in other Ascidians, consists of a very 

 complex lacunar network, including in its course certain sinuses, 

 in which the course of the blood cannot be regulated, except in the 

 walls of the " branchia," where the crossing of the sinuses at right 

 angles leads to a certain amount of regularity. This lacunar organi- 

 zation is the cause of the alternation of the direction of the blood. 

 The wall of the heart varies in different genera. Excepting the heart, 

 the blood-vessels have no proper wall. 



The elements of the blood resemble those found in the connective 

 tissue, and are of two kinds : one sort are analogues to lymph- 

 corpuscles ; the second are derived from the first, by degeneration, 

 and are formed of small concretions or granules. 



