A TAXONOMIC STUDY ON PYEOSOMA — METCALF AND HOPKINS. 217 



of anastomosing circum-oral fibers. These latter are generally not 

 present in young zooids (fig. 7, pi. 18)/ hence they seem to be of 

 secondary development. In the lateral muscular system one finds 

 ordinarily one ventral cross-strand in front of the endostyle (I. m.) 

 and a dorsal set of about three strands just in front of the ganglion 

 (I. m' .). The ventral strand branches once on each side of the zooid; 

 the three dorsal strands may branch once or twice on each side. In 

 many of the older zooids there is but one transverse band on the 

 dorsal side, and this does not branch greatly (fig. 3, pi. 16). The fact 

 that in this species the lateral muscular system is less developed in 

 many adult zooids than in the buds, and the further fact that this 

 system is always still more developed in P. spinosum, indicate that, 

 as regards the lateral muscles, P. agassizi is secondarily simplified. 

 The branches from the two sets of fibers do not unite distally, as in 

 P. spinosum. There is often a connection, however, between the 

 dorsal portion of the lateral musculature and the circum-oral rings, 

 by means of two connecting fibers, one on each side of the zooid (fig. 3, 

 pi. 16). The cloacal muscles, one lying on each side of the pharynx, 

 over the peribranchial chamber, are rather long and slender (fig. 3, 

 pi. 16). The dorsal end of each is connected with the ganglion by a 

 prominent unbranched nerve, the seventh (figs. 3, pi. 16, and 5, pi. 17). 

 There is a cloacal sphincter which is developed rather strongly on the 

 dorsal side of the aperture but scarcely at all on the ventral side (fig. 

 3, pi. 16). 



The pharynx. The oral aperture opens almost directly into the 

 branchial chamber proper. It is relatively wide and bears a promi- 

 nent fringe of true tentacles, these being fairly constant in number. 

 There is one median tentacle which is the longest, and 16 to 18 others, 

 arranged in most cases with an appearance of bilateral symmetry (fig. 

 2, pi. 16) . The branchial chamber proper is broad and elliptical. The 

 endostyle curves strongly near its anteroventral end. The dorsal 

 languets, about 5 or 6 in number, commence just at the posterior 

 termination of the peripharyngeal bands and continue back to the 

 esophagus (fig. 7, pi. 18). They are fairly long but never very promi- 

 nent. There are about 16 branchial bars, occasionally as many as 17, 

 and from 20 to 31 stigmatal rows, usually 26. The stigmata in this 

 species, instead of lying at right angles to the longitudinal axis of 

 the zooid, are so placed as to form an angle of 50° to 70° with this 

 axis; that is, the stigmatal rows run from the antero-ventral side of 

 the animal upward obliquely toward the postero-dorsal side. In the 

 following species (P. spinosum) this angle is even smaller, 5°-20°. 



Luminous organs (Z. o.). These are best seen in young, actively 

 growing colonies. They are variable in size and shape, usually 

 quadrangular or elliptical, and are not at all prominent. As the 



1 See to the contrary Neumann, 1909-1913, p. 92. 



