302 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



the rudiment which has arisen at the posterior end by the union of two 

 pouches. 



It is not necessary to enter into a minute analysis of his description, 

 for comparison of his figures with mine shows that he has been misled 

 by his erroneous conception of the primary position of the buds and has 

 mistaken the right and left pouches for dorsal and ventral. 



His more recent account (15, pp. 23-25) of the origin of the post- 

 pharyngeal gut of pyrosoma is very similar to what I have found in 

 salpa, for he says (pp. 615-622) that, while it arises as a pair of folds from 

 the pharynx, these soon unite to form an unpaired blind diverticulum, 

 which afterwards becomes differentiated into oesophagus, stomach and 

 intestine ; that its pharyngeal end becomes the oesophagus, while the 

 intestine arises from its blind end and ultimately acquires an anal 

 opening into the median atrium. 



Salensky's account of the origin of the gut in pyrosoma is quite 

 different, however, for he says (17, pp. 69-72) that it is bilateral in origin 

 and arises from a pair of folds from the sides of the aboral end of the 

 pharynx, which unite with each other to form a horseshoe-shaped canal. 

 If I understand his description, he holds that the right fold forms the 

 oesophageal portion of the gut and the left one the intestinal portion, and 

 that both open at first into the pharynx, although the intestine soon loses 

 this connection and acquires a new anal opening into the median atrium. 



SECTION 12. The Heart and the Eleoblast. 



The origin of the eleoblast of the solitary salpa is described on 

 pp. 37-39, and the origin of its heart on pp. 41 and 42. The heart and 

 the stoloblast of the aggregated salpa are formed from the mesoderm, 

 which is described in Section 8, p. 76, and the origin of the heart is 

 described on p. 83. 



In all the aggregated salpae which I have studied the stoloblast 

 arises as a pair of symmetrical rudiments, as is shown at K on pp. 81 and 

 82, cuts 0, P, Q, R and S. In Salpa pinnata these soon meet and fuse on 

 the middle line, but in Salpa cylindrica, Plate XXXIX, Figs. 1 and 6, k, 

 and in Salpa africana, they remain distinct even after all the other 

 organs of the body are fully formed. 



It is not recognizable as a distinct structure until the stage shown in 

 Plate V, Figs. 2 and 3, is reached, but I see no reason for doubting its 

 derivation from some of the mesoderm cells which are shown, uncolored, 

 between the perithoracic tubes and adjacent tissues, in Plate XXIII, Fig. 7. 



