Origin of the Organs of Salpa. 131 
statement, and says (p. 139) that while his studies of the 
embryo of Salpa pinnata have in other respects confirmed 
his account of the origin of the cloaca and gill of Salpa demo- 
eratica, 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 
runcinata (fusiformis) (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. 
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 longitudinal sections of embryos of 
Salpa runcinata which are shown in his plate xxiv. figs. 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 Pdmh in the younger 
