222 BULLETIN - 100, UNITED STATES NATIONAL MUSEUM. 



Digestive tract. This "nucleus" of organs is so placed that its 

 elongated axis is more nearly parallel to that of the zooid than in 

 any other Pyrosoma. The rotated position of the pharynx seems to 

 account for this. We find also that the intestine is greatly elon- 

 gated, the anus being located considerably posterior to the stomach. 

 The esophagus opens from the pharynx, between the posterior ends 

 of the stigmatal rows, by a broadly funnel-like aperture. It enters 

 the posterior side of the stomach, giving to this latter organ its broad, 

 bilobed appearance (fig. 9, pi. 20). 



In the region just anterior to the gut, the proliferating stolon 

 develops (s., fig. 8). Between the base of the stolon and the endo- 

 style one can sometimes observe an elongated tube, the pericardium, 

 with a dorsal invagination, the heart. 



The gonads can be found in the zooids of comparatively large colo- 

 nies only. The testis, composed of a large number of radiating seg- 

 ments (we counted as many as 77 in one case), is a flatly hemis- 

 pherical body lying posterior to, and between, the two limbs of the 

 gut. A sperm duct takes its origin on the upper (inner) side of the 

 testis and, passing back beneath the intestine as a dilated tube 

 narrowed at its distal end, it opens into the cloaca. At the edge of 

 the cloaca, and very near to the aperture of the sperm duct, the egg 

 is attached (ov. fig. 8) . This lies in a vescicle formed by the inner and 

 outer layers of the cloacal wall. Embryos were found of rather large 

 size, 1.5-2 mm. (fig. 11, pi. 21), but in only a few had the formation of 

 the four primary ascidiozooids more than commenced. The embryos, 

 whose stolons have segmented into four zooids, are much smaller 

 (0.6 mm.), having the yolk mass greatly reduced. It would seem 

 that this loss of volume of the yolk mass can not be due solely to its 

 having been used as food, but that it must have lost bulk also by 

 osmosis. All of these embryos were detached from the parental 

 ovaries. From this fact, and because of their large size, it seems 

 probable that they are customarily sent out of the colony at a very 

 early period in their development. The species is strongly pro- 

 tandrous. In zooids in which the testis has developed into a very 

 well-defined organ, with a duct, the egg has often just made its appear- 

 ance; and in maturer zooids, in which the egg is ripe, the testis may 

 be undergoing degeneration. This relation, of protandry in the 

 zooid does not preclude the possibility of self-fertilization within the 

 colony, for the various zooids mature at different periods. 



In our material from the Pacific Ocean we find an organ of prob- 

 lematic function, which may possibly have something to do with 

 reproduction. It is a roniform, vesiclelike organ attached by its 

 end to the outer surface of the body near the ventral edge of the 

 cloacal aperture (figs. 9 and 10, pi. 20). 



The cloaca in P. spinosum is very greatly modified, perhaps in 

 adaptation to the oblique position of the pharynx and digestive 



