236 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



the colony is smooth, except for these long, slender processes. At 

 the distal end of each process the surface of the test is raised into 

 papilla-like elevations, or denticles, each one containing a test cell 

 (fig. 29), and the oral aperture is surrounded by an overhanging wall 

 of the test. In a longitudinal section (fig. 28) the test process is 

 seen to be truncated obliquely so that the mouth opens somewhat 

 ventrally. 



A loose and irregular arrangement of zooids obtains. Occasionally 

 a zooid will be found to be turned from its normal position, so that 

 its ventral side is directed toward the aperture of the colony. The 

 majority of individuals in the colony — that is, those lacking the 

 oral processes — are about 5 to 7 mm. long (fig. 27). Those with 

 the oral siphons well developed attain a maximum length of 19 mm., 

 the siphon then measuring about 14 mm., or three-fourths of the 

 total length of the entire zooid (fig. 26). The inner epithelium of the 

 oral siphon is dotted with large, star-shaped and highly branching 

 pigment cells of a reddish color. In addition to the pigment cus- 

 tomarily found on the follicle of the testis there are scattered pig- 

 ment cells on the inner ectodermal wall of the cloaca, in the region 

 of the viscera. The occurrence of pigment cells in the cloacal region 

 has been observed in no other forms except P. aJierniosum and some 

 varieties of P. atlanticum, and in the latter species they are not prom- 

 inent. 



The branchial chamber proper is oval or oblong, higher (dorso- 

 ventrally) in front than at its posterior end. The endostyle is only 

 slightly curved. In each branchial lamella there are 38 to 40 rows 

 of stigmata and about 18 longitudinal bars. Dorsal languets, for 

 the most part 9 to 10, sometimes as many as 12. 



The luminous organs are small, elliptical bodies, lying equidistant 

 from the dorsal and the ventral mid-lines of the zooid. 



The digestive tract is rather large and prominent The esophagus 

 has a broadly funnel-shaped aperture; it enters the triangular stom- 

 ach at its posterior side. In other respects the digestive tract is as 

 usual. The cloaca is broad, and its two lateral muscles are long. 



Gonads. The testis, consisting of about 30 lobes, causes only a 

 very slight bulge in the ventral body wall. Consequently it extends 

 upward so as to inclose the loop of the intestine. Just to the right 

 of the testis and a little behind it is the ovary. This species is 

 protandrous, but the degree of protandry which obtains is not so 

 great as in other Pyrosomas (as P. atlanticum giganteum). In colonies 

 3 or 4 centimeters long, made up of numerous zooids, only a very few 

 individuals can bo found from which the embryos have been set free. 

 Hence it seems probable that older colonies of this species will be 

 found even larger than those already collected. 



P. ovatum occurs in the Indian and South Atlantic Oceans. 



