W. G. YanName — Bermuda Ascidians. 391 



bars between the last fold and the dorsal lamina. There are from 

 seven to ten bars between the base and summit of a fold, varying 

 according to its breadth. 



The transverse vessels are of four or five sizes : the smallest cross 

 the stigmata at their middle point without interrupting them. In 

 general they are arranged according to the same scheme as the ten- 

 tacles, a vessel of a given size being located midway between two of 

 the next larger size, but many irregularities occur. The transverse 

 vessels become thicker as the dorsal lamina is approached. 



The above may be taken as the average condition of the branchial 

 sac in a fully adult specimen. Considerable individual variation 

 occurs in the distribution and number of internal longitudinal bars 

 on the folds and interspaces, and in the number of stigmata in the 

 meshes formed by them. In many examples it averages one or two 

 less than in the specimen shown in fig. 69. Figs. 147 and 149 show 

 a part of the sac of such a specimen. 



Such variations are merely individual peculiarities. In addition, 

 there are also differences due to the age of the animal. The branch- 

 ial sac in the individual shown in fig. 78 did not differ materially in 

 structure from those of larger specimens, but when still smaller and 

 evidently immature specimens are examined, the structure of the sac 

 is found to be more or less simplified. One or more of the folds 

 may be wanting or present only in a rudimentary condition, and the 

 number of internal longitudinal bars, as well as of the stigmata, 

 becomes reduced. 



The intestinal loop is small and the intestine doubles back so that 

 it comes in contact with the stomach near the middle of that organ, 

 or a little posterior to the middle. The rectum is long and its open- 

 ing has about a dozen rounded lobes, or more strictly, plications of 

 the edge. The stomach is of a brownish orange color, and'has from 

 18 to nearly 30 longitudinal folds in its wall, the number varying 

 according to the age and size of the individual. 



The ovaries consist of stout glandular tubes, usually two on each 

 side (one of which may be forked). They pursue a more or less 

 crooked course from near the endostyle (on the left side from near 

 the intestine) and end near the atrial siphon. The sperm ducts accom- 

 pany them and the openings are close beside those of the oviducts. 

 In some specimens both orifices may be seen to have a lobed or pli- 

 cated margin similar to that of the rectum, but the lobes are smaller. 

 The testes are elongated, more or less branched organs of small size 

 with enlarged ends. They are arranged along each side of the ova- 



