A TAXONOMIC STUDY ON PYROSOMA — METCALF AND HOPKINS. 225 



the ganglion (fig. 4 B, p. 206), and is shorter than among the Pyro- 

 somata fixata. An idea of the distribution of the nerves may be gained 

 from figure 13. It will be seen that the fourth and sixth nerves are 

 least prominent. The cloacal muscle is innervated by the fifth and, 

 in part, by the eighth nerve, the atrial sphincter by the seventh, the 

 last pair (eighth) being large and important. 



The pigment cells, found to some extent in the zooids of all Pyro- 

 somas, are sometimes quite conspicuous in the members of this sub- 

 genus. In some species they occur in masses on the viscera; in others, 

 as large, star-shaped cells scattered over the walls of the prebranchial 

 or of the cloacal chamber (fig. 25, pi. 24). 



The cloaca may be short and broad (fig. 17, pi. 23), but ordinarily it 

 is elongated, and has a small, circular aperture (pi. 29). 



Two cloacal muscles (el. m.) lie one on each side of the common 

 cloaca (pis. 30 and 31). There is no lateral muscle system, as in the 

 Pyrosomata fixata, but there are two or three circumoral fibers, which 

 do not- branch and anastomose (pis. 26 and 27). Oral and cloacal 

 sphincter muscles are present as simple, closed rings (fig. 36, pi. 29). 



The gonads occupy positions ventral to the digestive tract, and 

 generally quite distinct from it. The testis lies on the left side, the 

 ovary on the right (fig. 31, pi. 27); both develop at about the same 

 time, or one in advance of the other (protandry or protogyny ) . There 

 are relatively few (12-30) lobes in the testis, and these project inward. 

 The embryo is retained in the ovary until fairly late in its develop- 

 ment. When released, it continues its growth in the cloaca, in those 

 species in which the cloaca is large, or in the right peribranchial space, 

 if the cloaca is short. The majority of the forms are rather small, 

 hence mature their sexual products relatively early. 



PYROSOMA VERTICILLATUM (Neumann, 1909, c). 



Plate 21, fig. 12; plate 22, fig. 13. 



This species was first taken from the Indian Ocean (Feb.-Mar., 1899, 

 Deutsche Tief see-Expedition). Twenty-one colonies in all were col- 

 lected, and have been described as representing a distinct type of 

 Pyrosoma. They were characterized by their unique form, but more 

 especially by the regular arrangement of zooids which obtains, even 

 in adult colonies. 



Specimens taken by the Albatross in Philippine waters in 1908- 

 1909, though undoubtedly belonging to this species, yet appear to 

 differ from those described by Neumann. Since these points of 

 difference are constant throughout the entire Albatross collection— 

 of twenty specimens from five stations— it has seemed best to treat 

 this new type as a variety of the present species. In variety cyclin- 

 dricum, as we name it, the colony is relatively longer— that is, more 

 7911—19 3 



