228 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The mouth and its associated parts are simple, probably affording 

 typical conditions for the subgenus, since there appear to be no 

 muscles or nerve fibres which have become modified through over- 

 growth or atrophy. The inner border of the mouth is fringed with 

 a variable number (usually 18) of small folds erroneously called ten- 

 tacles; and on the ventral edge there is a median tentacle with a 

 vesicle-like enlargement at its base. The whole constitutes what 

 Huxley called the "tentacular fringe." Surrounding the mouth and 

 fringe there is an oral sphincter muscle, and outside of this two deli- 

 cate, circum-oral fibres. The nerves about the oral region are rather 

 easily traced and identified. 



The branchial basket shows about 14 longitudinal bars on each 

 side, and from 27 to 28 rows of stigmata. This serves to distinguish 

 this variety from P. verticillatum proper, in which the number of bars 

 is about 11, and the stigmatal rows about 21. The number of the 

 dorsal languets, five, seems to be constant in adult individuals. The 

 endostyle is typical but short, making a strong, even curve along 

 the ventral side of the pharynx. The digestive tract appears very 

 narrow; the intestine makes a sharp bend upon itself instead of the 

 wider, customary loop (see P. atlanticum ailanticum). The two dorsal 

 leucocyte masses are distinct from each other. They are short and 

 not very conspicuous. The luminous organs are usually oval and 

 elongated dorso-vcntrally. 



The reproductive organs bear about the same relation to the zooid 

 as is characteristic of the species type. The testis causes the posterior 

 wall of the body to bulge somewhat, often projecting considerably. 

 Its lobes, about 15 in number, are directed nearly forward, or diago- 

 nally forward and upward; they rarely form a compact organ but 

 lie rather open, and in the form of a rosette. As before mentioned, 

 the cloaca is very short and broad. Its aperture is also broad, there 

 being scarcely any diaphragm, so common in other Pyrosomas. Cor- 

 respondingly we find the cloacal muscle long and narrow. The ovary 

 lies to the right of the testis as usual, developing ordinarily much 

 before the latter, so that the zooids would be described as protogynous. 

 In agreement with the observations of Neumann upon P. verticil^ 

 latum, we find that in the variety cylindricum the primary ascidi- 

 ozooids and the earlier formed buds maybe protandrous; at least the 

 testis makes its appearance first in the early zooids of this variety. 



Embryos in the four primary zooid stage, tetrazooid colonies, or 

 "Viererkolonien," were found in the right peribranehial spaces of 

 several zooids. Some, less developed, were still fixed in the wall of 

 the cloaca. Embryos with unsegmented stolons measure 0.6-0.9 mm. 

 in diameter; those with the stolon dividing into four zooids are about 

 0.6 mm. in diameter. There is therefore no rapid shrinking in this 

 embryo such as occurs in those of P. spinosum. 



