Zool.— Vol. I.] BANCROFT— CHELYOSOMA PRODUCTUM. 327 



This is apparently the plane adopted by Drasche (i£ 

 Herdman (1891), and Traustedt (1880). But the last 

 author in a later paper (1882) defined the sagittal plane as 

 passing through the endostyle and ganglion. As in C. 

 macleayanum the endostyle is near the extreme left, and 

 the ganglion on the right of the line joining the siphons; 

 this plane is nearly parallel to the disk, the siphons are on 

 the left, and the viscera on the right side. Though on 

 some grounds this criterion might be justified for C. 

 macleayanum, it will hardly serve for the more elongated 

 C. -productum, in which this sagittal plane would neither 

 contain the long axis of the animal nor divide it into 

 approximately equal parts. 



Both Drasche for C. productum and Herdman for the 

 whole genus disagree with Traustedt in describing the 

 viscera as located on the left side of the animal, and Kiaer 

 (1893) makes the strange statement that both disk and 

 digestive tract are on the left side. The evidence for some 

 of these statements is seen in the figures of Eschricht 

 (1842), Traustedt (1887), and Wagner (1885). These 

 show that in C. macleayanum the viscera are either 

 strictly ventral in position or slightly on the left of 

 the median line. In C. prodicctum, on the other hand, 

 the specimens that I have examined fail to confirm 

 Drasche's statement, for in them the major part of 

 the digestive tract is on the right side of the sagittal plane 

 (fig- J 3)> an d this condition is more pronounced in the 

 more elongated individuals. In the flattest of my speci- 

 mens, however, the conditions found in C. macleaynum 

 are more closely approximated. But more important than 

 the question of determining whether two-fifths or three- 

 fifths of the viscera are on the right of the midventral line 

 is the fact that in both species all of the digestive tract, 

 except the dorsal terminal part of the intestine, is ventrally 

 situated. 



Although Chelyosoma, since its viscera are sometimes on 

 one and sometimes on the other side of the median plane, 

 shows how the change from the Corella to the Ascidia 



