STUDIES ON THE PEOTOCHOEDATA. 351 



venstadium, wenu also von einer Riickbildung im Schwanze 

 keine Spur ist." 



In Ciona I have noticed the first rudiment of the longi- 

 tudinal musculature at a stage a trifle later than that repre- 

 sented in figs. 2 and 3. The first muscular band proceeds from 

 the base of the atrial siphon of each side, and seems to be at 

 first continuous with a portion of the sphincter muscle of the 

 siphon. 



Very soon, however, it becomes quite independent of the 

 latter and extends in length, and finally consists of a single 

 longitudinal band bifurcated anteriorly, one branch proceeding 

 to the region of the buccal siphon, and the other to the ante- 

 rior region of the atrial cavity (fig. 5). Later on new mus- 

 cular bands arise, and at a stage with six transverse rows of 

 stigmata the longitudinal bands, about seven in number, are 

 distributed over the body-wall on each side in a spreading, 

 tree-like fashion ; but posteriorly they all converge together, 

 to be inserted at a definite point on each side of the stolon of 

 fixation, which was the prseoral lobe before the change of 

 axis, near to its base of attachment to the body of the 

 Ascidian. 



By means of these longitudinal muscles the young Ciona 

 can bend itself double ; that is to say, it can contract itself 

 ventralvvards, so as to lie approximately at right angles to the 

 fixing stolon. The formation of these longitudinal muscles is 

 the first commencement of the muscular mantle of the adult. 



9. Pericardium and Heart of Ciona intestinalis and 

 Clavelina lepadiformis. 



I am able to confirm van Beneden's and Julin's account of 

 the endodermal origin of the pericardium in Ascidians, and 

 of the absence of an endothelium in the wall of the heart. 



In Ciona the pericardium arises at a later period than in 

 Clavelina, and it is only with a knowledge of what occurs in 

 Clavelina that the endodermal origin of the pericardium could 

 be affirmed for Ciona. I have seen the epicardium in Clavelina 

 which was described by van Beneden and Julin, but no tracQ 



