226 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



slenderly cylindrical — and there are numerical distinctions — as 

 regards number of stigmata, and the like — to be described later. 



The colony of P. verticillatum is typically egg-shaped, occasionally 

 somewhat elongated. The largest is but 3 cm. long, so that it is 

 probable that this form reaches a definitive length seldom exceeding 

 2.5 cm. The zooids are arranged in transverse, parallel rows, or 

 verticils; the spaces between the zooids and also between the rows 

 are relatively great. Test-processes are completely lacking, and the 

 test itself is firm, smooth, transparent, and colorless. The oral 

 apertures are considerably sunken beneath the surface of the colony, 

 so that there is a funnel-like depression in the test leading down to 

 each. 



Mature zooids are 2.5-2.7 mm. long from mouth to cloacal aper- 

 ture, 2.7-3 mm. high, i. e., in dorso-ventral measurement. They vary 

 only slightly in size throughout the colony. The branchial basket in 

 this form is quite short and is relatively simple in its make-up. There 

 are about 21 dorso-ventral rows of stigmata on each side of the 

 branchial chamber, and about 1 1 longitudinal bars. Dorsal languets, 

 4-5. There is only a very short cloacal chamber, the two peri- 

 branchial pouches opening almost directly into the colonial cavity by 

 the very wide atrial opening. The cloacal muscle is long and narrow. 



Gonads. The testis is described as consisting of from 12 to 15 

 lobes, lying rather more on the posterior than on the ventral wall of 

 the body, and scarcely bulging beyond the general contour of the 

 body. The egg is said by Neumann to mature earlier or sometimes 

 later than the testis. This statement is based upon his own and upon 

 Seeliger's observations, namely, that even in those species whose 

 zooids are ordinarily strongly protogynous, the four primary ascidio- 

 zooids, and a few of the later formed zooids, may ripen their sperma- 

 tozoa first. Protogyny within the individuals of the colony seems to 

 come about progressively from an original condition of protandry as 

 new zooids are formed by budding. Thus the possibility of self- 

 fertilization in this species (considering the colony as the individual) 

 is not precluded. Nevertheless it should be strongly emphasized that 

 in this and some of its nearly allied forms, protogyny is the rule for 

 most of the zooids within the colony. In others, to be described 

 later (as subspecies of P. atlanticum) , there is even an approach to a 

 condition of protandry in many zooids. For the most part the male 

 and female sex-cells in the zooids of P. atlanticum and its several sub- 

 species ripen at nearly the same period, although here also there is 

 progressive maturing of the sex-cells from one end of the colony to 

 the other. 



The characteristics of P. verticillatum are given by Neumann as 

 follows: the funnel-like oral depressions in the otherwise smooth 

 surface of the test, the height (dorso-ventrally) of the zooids, the 



