20 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Odacnemus as an aberrant offshoot from the primitive Ascidians, 

 whose nearest extant relatives are the Clavelinidae. 1 To this classi- 

 fication Hitter (1906, a) has given his approval, and Herdman 

 (1904) has recently expressed his agreement. 



Above the neural gland, on each side, are two outgrowths from the 

 ganglion, one of small cells continuous with the smaller cells of the 

 ganglion itself (fig. 8, b), the other a mass of large cells (b') like the 

 larger cells of the ganglion. Both these masses of cells arise as out- 

 growths from the ganglion. The small-celled group retains its con- 

 tinuity with the ganglion. The large-celled group, on the other hand, 

 is distinct from the ganglion, but is connected with it by numerous 

 well-developed nerve fibres. 



Many have studied the solitary form of Cyclosalpa pinnata. There 

 are some discrepancies, for the most part slight, between our work 

 and that of others, but it seems hardly well to burden this paper with 

 a detailed discussion of these discrepancies. It is doubtful just how 

 far the differences in description may be taken as indicating variation 

 in structure in the species, and to what extent allowance must be made 

 for the personal equation of the observers. In our observation of 

 many specimens from the Atlantic Ocean and from the Mediterranean 

 Sea we have found the structure uniform as we describe it. The very 

 careful work of Streiff upon the muscles agrees with our observations, 

 except in two minor regards. He does not show contact between the 

 fourth oral sphincter muscle of the dorsal lip and the horizontal band 

 which runs up and back to join the dorsal portion of the intermediate 

 muscle. In other species we have found divergence in the near 

 approach or actual connection of such accessory muscle bands, and 

 we do not doubt the accuracy of Streiff' s description. He does not 

 show the diagonal second atrial sphincter which we have described 

 as showing a rudimentary atrial retractor arrangement. We find no 

 other authors' figures sufficiently accurate in detail for profitable 

 comparison of this point. All our specimens show the condition 

 which we figure. 



CYCLOSALPA PINNATA, aggregated form.' 



Plate 1, figs. 3 and 4; plate 2, figs. 5, 7, and 8. 



The aggregated form of Cyclosalpa pinnata is shown in figure 3, 

 which gives a view from the right side. One observes the presence 

 of a stalk of attachment, or peduncle, by which the individual was 

 joined with the other zooids into a whorl. Postero-ventrally the 

 visceral region of the body is bulged out, the single intestinal caecum 

 pushing out into a slight evagination of the mantle, suggesting com- 

 parison with the visceral protuberance ("post-abdomen" of Ritter) 

 seen in Cyclosalpa jloridana (pi. 5, fig. 15), C. baJccri (pi. 8, fig. 21), 



i See Metcalf (1900), p. 579. * United States National Museum Collection. Cat. No. 6461. 



