294 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



He describes the atrium and " gill " as arising in a totally different 

 way in Salpa africana, pp. 160 and 163; Salpa pinnata, pp. 338-39, and 

 Salpa runcinata (fusiformis), p. 354, for while he says that in these 

 species, as in Salpa democratica and Salpa pinnata, the atrium is part 

 of the pharynx, it is separated off by two folds, Taf. 24, Figs. 7 and 8, 

 Kestp, of its lateral walls, which grow towards each other and unite on 

 the middle line to form a horizontal diaphragm, which shuts off the 

 dorsal division of the pharynx from the ventral chamber. This dia- 

 phragm then becomes separated at its sides from the lateral walls of 

 the pharynx, so that a secondary communication is established on each 

 side between the upper and lower chamber, while the middle portion of 

 the .diaphragm becomes the gill. It will be seen that according to this 

 account the "gill" of Salpa democratica and Salpa pinnata arises as an 

 unpaired, median, dorsal fold, while in the other species it arises as a 

 pair of lateral folds; in the first two species the gill-slits, or openings 

 by which the two chambers communicate at the sides of the gill, are 

 primary, while in the others they are secondary; in the first two the 

 atrium is a secondary chamber formed by the union of two pharyngeal 

 pouches, while in the other species it is primary. 



The reconciliation of these statements with each other seems impos- 

 sible, and any attempt to bring all or any of them into accord with my 

 own account seems hopeless. More critical examination will show, how- 

 ever, that his observations are rather imperfect than inaccurate, and 

 that his errors are errors of interpretation. 



My own observations show that the perithoracic tubes and atrial 

 chamber are formed before the cavity of the pharynx is hollowed out 

 in the mass of visceral follicle cells ; and Salensky has, in these early 

 stages, mistaken them for the pharynx or " primitive digestive cavity." 

 This is well shown by the comparison of the two figures of longitudinal 

 sections of embryos of Salpa runcinata, which are shown in his Plate 

 XXIV, Fig. 4 and Fig. 9. These figures show clearly that the so-called 

 "Darmhohle," Pmd, of the younger embryo is the atrium, and not the 

 pharynx, of the older one. This is proved even more conclusively by 

 comparing his Fig. 11 of Plate VIII with Fig. 5; for the chamber 

 which is marked Pdmh in the younger embryo is obviously the one 

 marked Kl in the older one. 



The perithoracic tubes are actually shown in many of his figures, 

 notably in his Plate 6, Fig. 5, pin, where they are marked Drm. They 

 are also shown in his Plate 12, Fig. 24, at Dh, and their union on the 



