Origin of the Organs o/ Salpa, 131 



statement, and says (p. 139) that while his studies of the 

 embryo of Salpa pinnafa have in other respects confirmed 

 his account of the origin of the cloaca and gill of Salpa demo- 

 cratica, they show that the gill is in its origin a hollow diver- 

 ticulum from the body-cavity. He here describes the cloaca 

 and gill as arising in a totally different way in Salpa africana 

 (pp. 160 and 163), Salpa punctata (pp. 338, 339), and Salpa 

 Tuncinata {fusiforrnis) (p. 354) ; for while he says that in 

 these species, as in Salpa democratica and Salpa pinnata, the 

 cloaca is part of the pharynx, it is separated off by two folds 

 (Taf. xxiv. 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 cloacal 

 division of the pharynx from the ventral chamber. The 

 diaphragm 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 the 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 he describes it in the other species 

 as arising from a pair of lateral folds ; in the first two species 

 the gill-slits or openings by which the two chambers commu- 

 nicate at the sides of the gill are primary, while in the others 

 they are secondary ; in the first two the cloaca is a secondary 

 chamber formed by the union of the two pouches from the 

 pharynx, while in the other species it is primary. 



It does not seem possible to reconcile these statements with 

 each other, and any attempt to bring all or any of them into 

 accord with my own account seems hopeless. More critical 

 examination will show, however, that his observations are 

 rather imperfect than inaccurate, and that his errors are errors 

 of interpretation. 



]\ly 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 longitudinal sections of embryos of 

 Saljia runcinata which are shown in his plate xxiv. tigs. 4 

 and 9). These figures show clearly that the so-called 

 " Darmhohle " [Pmd) of the younger embryo is the cloaca, 

 and not the pharynx of the older one. This is proved even 

 more conclusively by comparing his fig. 3 of plate viii. with 

 fig. 5, for the chamber which is marked Pdnih in the younger 



