82 



JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



The aboral ends of the pharyngeal pouches elongate, as is shown in 

 cuts O and P, 27 and 28, and, bending towards each other, cut Q, finally 

 meet on the middle line and unite with each other, as shown in cut R, 

 27-28, to form the aboral portion of the pharynx. They are shown in 

 contact but not yet united, in Plate XXXIII, L~L', Figs. 3, 4, 5, 27 and 

 28, while in M-M' and N-N', Figs. 3 and 4, they are united on the middle 

 line of the ventral surface. 



Both the oral and the aboral ends of the pouches ultimately unite on 

 the middle line throughout their whole length, so that, as is shown in 

 cut S and cut X, the pharynx becomes a large, unobstructed chamber, 



CUT R. 



OUT S. 



opening to the exterior at the mouth, and communicating with those of 

 adjacent salpa3 through the opening which is marked d' in the figures. 



(3) The perithoracic tubes and cloaca. As the pharyngeal pouches 

 grow backwards they carry with them, on their dorsal sides, the peri- 

 thoracic vesicles, g and h, as is shown in cut N. At about the stage shown 

 in cut 0, each of these vesicles unites with the dorsal surface of the 



