224 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



posterior end of the endostyle (fig. 30, pi. 26 and fig. 32, pi. 27). 

 Only one bud is produced at a time, for as soon as one has formed 

 it is set free and a new bud develops from the remainder of the 

 stolon. After separating from the parent zooid the young bud is 

 moved dorsalward or toward the aperture of the colony, through 

 the agency of special test cells given off from the dorsal side of the 

 bud. These wandering buds take positions dorsal to the next older 

 tier of zooids. In young colonies they arrange themselves symmet- 

 rically, 1 coming to lie opposite the interspaces between the parent 

 zooids (figs. 50, 52, and 53, pi. 36). Some species preserve this 

 regular arrangement (figs. 43 and 44, pi. 33); others lose it, usually 

 rather early (pis. 34 and 35). A result of this manner of colony 

 formation is that the four primary ascidiozooids remain at the closed 

 end of the colony, new buds continuing to form around the open 

 end of the colony until a certain stage is reached (see p. 212). 



There are two tunic vessels developed in connection with each 

 primary ascidiozooid, but only one from each of the subsequently 

 formed buds. 



The colony. The test is generally of rather firm, cartilaginous 

 texture. It is transparent, usually colorless, but sometimes a little 

 stained, probably from pigment contained in the zooids. There are 

 no " guarding" processes of the test surrounding the colonial aper- 

 ture, but a diaphragm is generally present and well developed (fig. 

 46, pi. 34). Many species have test-processes over the general sur- 

 face of the colony, in the form of conical protuberances, through 

 which the oral siphons of the zooids project so as to open near their 

 outer ends (pis. 34 and 35; fig. 24, pi. 24; fig. 26, pi. 25; fig. 30. 

 pi. 26). Sometimes the general surface of the test is denticulate or 

 roughened. 



Zooids. The rows of stigmata are not oblique, but run at right 

 angles to the longitudinal axis of the zooid. In most cases the 

 branchial basket is elongated in the direction of this axis. The 

 oral aperture bears a median, ventral tentacle, and a rather definite 

 number of tentacle-like folds or swellings, forming a circlet around its 

 inner border (fig. 13, pi. 22). The prebranchial chamber may be 

 short (pi. 23) or be elongated as an oral siphon (fig. 26, pi. 25). The 

 peripharyngeal bands unite at a broad angle directly beneath the 

 ganglion (fig. 13, pi. 22). A single pair of luminous organs, at the side 

 of the peribranchial chamber, is always present. The blood-forming 

 organ is present as a conspicuous, elongated mass of cells on the 

 dorsal side of the zooid. 



Nervous system. In this subgenus the ganglion is smaller (fig. 13, 

 pi. 22). The duct of the subneural gland runs obliquely forward from 



' See Neumann, 1909, c and 1909-1913, (or a fuller accouDt. 



