W. K. BROOKS ON THE GENUS SALPA. 



lor, 



CUT W. 



CUT X. 



It is plain that, as there are no connecting tubes, the part of the 

 body of each salpa which is joined to those before and behind it must 

 retain its original place in the axis of the stolon, while the only struc- 

 tures which are free to move are those at the oral and aboral ends of the 

 body. The salpa which pushes out to the right will therefore take the 

 shape which is shown in diagram W. The body becomes divided into 

 two distinct regions: 1st, the oral and aboral ends with the ganglion 

 s, the reproductive organs w, the oral ends 27 and 28, o, of the pharyn- 

 geal pouches, and their aboral ends 27 and 28, ab, with their peri- 

 thoracic vesicles g and li ; and 2d, the middle region of the body which 

 still maintains its connection with those of 'adjacent salpse, and consists 

 of an endodermal tube d' and the oral and aboral blood spaces. As 

 the diagrams show, the endodermal tube d' retains its connection with 

 the pharyngeal pouches, and at this stage the only communication 

 between the pharyngeal pouches of the two sides of the body is through 

 the endodermal tube d 1 . 



In this way each salpa becomes divided into a lateral portion, which 

 ultimately becomes completely shut in by ectoderm and separated from 



