. Bulletin - United States National Museum. Science. Fig. 94.—Iasis zonaria, solitary form, sagittal sec- tion OF THE ATRIAL APERTURE AND THE ADJACENT TIS- SUES, x 8 diameters. (Drawn by Hoyt S. Hopkins.) opening, this second ventral sphincter is continuous with the third dorsal atrial sphincter (a. s. 3) which starts as a single band, but soon breaks up into fine strands that form something of a reticulum. Several strands from this reticulum run for- ward to join the atrial re- tractor. These are independ- ent of the main trunk of the third dorsal sphincter, and may represent a fourth dorsal
. Bulletin - United States National Museum. Science. Fig. 94.—Iasis zonaria, solitary form, sagittal sec- tion OF THE ATRIAL APERTURE AND THE ADJACENT TIS- SUES, x 8 diameters. (Drawn by Hoyt S. Hopkins.) opening, this second ventral sphincter is continuous with the third dorsal atrial sphincter (a. s. 3) which starts as a single band, but soon breaks up into fine strands that form something of a reticulum. Several strands from this reticulum run for- ward to join the atrial re- tractor. These are independ- ent of the main trunk of the third dorsal sphincter, and may represent a fourth dorsal atrial sphincter. The third ventral atrial sphincter (v. s. 3) has no connection with mus- cles of the dorsal atrial lip, but is united by two branches to the middle portion of the atrial retractor. The dorsal lip of the atrial aperture is in two parts. The first, a slightly developed flap, at a lower level, bears dorsal sphincter No. 1. Dorsal sphincter No. 2 is not connected with any other muscle. It lies in the upper division of the upper lip. It is interrupted on the mid line, its two ends being bent forward. The upper portion of the dorsal lip has its test developed to form two triangular stiffened areas, just beneath which lies the reticulum formed by the strands of the third and fourth (?) dorsal atrial sphincters. The vertical section of this region shown in figure 94 should help to make these structures clear. The gut forms a rather close circular loop (figs. 90 and 94), but is much less compact than in Apsteinia and Salpa proper. It is much like Apstein's figure of the gut in Brooks i a rostrata (fig. 23, p. 51). In the character of its eye and the outgrowths from its ganglion (figs. 95 and 96),the soli! ary form of Iasiszonaria is one of the most aberrantof thesolitary Salpidae. Indeed, with the exception of RiUeria hexagona, it is the only species in the solitary form of which these structures depart markedly from the usual type. The eye has. Fig. 95.—Iasis zona
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