vol. 2, pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 133 



CU 



V.S.J 



V.S.. 



runs toward the atrial retractor. The end of this branch and the 

 tip of the atrial retractor are connected by a blood lacuna. 



The gut, as in the Thalias (fig. 104, p. Ill), is a close loop, almost 

 as compact as in the true Salpae. The course of the wide intestine 

 can however be made out without dissection. 



The eye shows the customary horseshoe form. Its rod-cells are 

 irregularly polyhedral, with unevenly thickened walls, that is, they 

 are degenerate. The neural glands are of the usual type. There are 

 large-celled and small-celled pairs of outgrowths from the ganglion, 

 just above and in front of the disks of the glands. 



PEGEA CONFEDERATA, aggregated form. 



The muscles of the aggregated Pegea confederata (fig. 123) show a 

 closer resemblance to those of the solitary form than is the case in any 

 other species of Salpidae. 

 There are four body muscles, 

 in two groups, on the dorsal 

 surface, often hardly reaching 

 to the sides of the body. The 

 intermediate muscle and the 

 oral musculature (fig. 124) 

 are as in the solitary form, 

 except for minor details 

 which comparison of the fig- 

 ures will show. 



The atrial musculature in 

 my very numerous specimens 

 is as shown in figure 125. 

 There is a well-developed 

 atrial retractor giving rise 

 above to the broad third dor- 

 sal sphincter muscle, which, 

 by the way, is interrupted on each side. There is a delicate ad- 

 marginal dorsal sphincter, also interrupted on each side, and a second 

 dorsal sphincter, which is very incomplete, being represented only 

 by a short branch on each side. The first and second dorsal sphinc- 

 ters are united below into a broad band which lies external to the 

 third dorsal sphincter and atrial retractor. The admarginal ventral 

 sphincter arises by two roots, one from the posterior edge of the 

 third dorsal sphincter, at its junction with the atrial retractor, the 

 other from the ventral edge of the common portion of the first and 

 second dorsal sphincters. These two roots soon unite to form the 

 single admarginal ventral sphincter. A second ventral sphincter 

 muscle (v. s. 2) corresponds to the basal atrial sphincter of other 

 species, only its ventral half being present in Pegea (see fig. 3, pi. 1, 



Fig. 122.— Pegea confederata, adult solitary form 

 atrial musculature of the left half of the body, 

 from a preparation similar to that from which 

 text figure 122 was drawn. x 12 diameters. 



