300 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



In Salpa pinnata the endostyle does not make its appearance until 

 the halves of the pharynx are completely united with each other, and 

 Plate XXXVI, Fig. 9, is the youngest stage in which I have found it in 

 this species. The persistency of the mesentery in Salpa cylindrica 

 enables us to discover that the right half of the endostyle is formed in 

 the right pharyngeal pouch, and the other half in the left. In Plate XL, 

 Figs. 14 and 15, the left half, d 2, of the endostyle of the right-hand salpa, 

 and the right half, d 1, of the left-hand salpa, are shown diverging from 

 the other halves and passing on to the far side of the stolon. 



The post-pharyngeal gut arises as a blind diverticulum from the 

 aboral end of the right pharyngeal pouch, 27, as is shown at q in Plate 

 V, Fig. 3, for a right-hand salpa, and at q in Fig. 4 for a left-hand salpa. 

 The part of this diverticulum which joins the pharyngeal pouch becomes 

 the oesophagus, and the stomach and intestine are developed from its 

 blind end. In all the species I have studied, the intestine bends to the 

 left around the stomach to open directly into the median atrium, and 

 the digestive tract assumes the form shown in Plate VIII, Fig. 2, and 

 Plate XXXIX, as already described, page 187. As the gut arises in both 

 the right-hand and left-hand salpae from the right-hand pharyngeal 

 pouch, and since the distortions which are produced by pressure and by 

 the changes of position affect the right-hand pouch of a right-hand salpa 

 just as they do a left-hand pouch of a left-hand salpa, and as they affect 

 the other pouch in quite a different way, the superficial history of the 

 gut in a right-hand salpa is quite different from its superficial history in 

 a left-hand one, although fundamentally they are exactly alike. 



While Salensky, in his first paper on the budding of salpa (Morph. 

 Jahrbuch, II, 1877), describes the endodermal tube, he says that it takes 

 no part in the construction of the salpa3, and that their digestive organs 

 are derived from that part of the stolon which I have called the genital 

 rod. Seeliger, a few years later, (11), p. 14, pointed out Salensky's error, 

 which he has himself admitted in a recent paper, (17), p. 78. 



Seeliger's account (11) of the origin of the endodermal tube and the 

 digestive organs is given on pp. 14, 18, 26-34 and 54-62. He shows, p. 14, 

 that the endodermal tube of the stolon is derived from the pharynx of 

 the embryo, with which it at first communicates. He says that this 

 connection is soon lost, but I have shown, p. 71, that it persists at all 

 stages in the history of the stolon of Salpa pinnata and Salpa cylin- 

 drica. 



