152 University of California Publications in Zoology. [Vol.6 



found in S. pinnata and 8. cylindrica, I quote from his descrip- 

 tion (Brooks. '93. p. 78) and then point out certain particulars 

 in which S. fusiformis-runcinata differs. 



"The first indication of the segmentation of the stolon is a 

 series of ectodermal folds, which first appear at the sides, but 

 soon extend up and down and completely encircle it, and push- 

 ing inwards, mark out the body cavities of the salpae and also cut 

 up the tubular structures inside the stolon into segments. 



"The active agent in this process of segmentation is the 

 growth of the ectodermal folds, and the other structures are 

 actually cut by these folds. 13 - As the result of this process, the 

 nerve tube becomes cut up into a series of ganglia, one for each 

 salpa, the perithoracic tubes become cut up into a series of peri- 

 thoracic vesicles, two for each salpa ; the genital string becomes 

 cut up into a series of eggs, one for each salpa, inclosed in a 

 follicle; and the thickened endodermal epithelium at the sides 

 of the endodermal tube, becomes cut up into a series of vertical 

 poiiches or pockets, two for each salpa, the rudiments of the right 

 and left halves of the pharynx." 



"At this stage each salpa is bilaterally symmetrical, and its 

 plane of symmetry is the same as that of the stolon, while 

 its long axis is at right angles to that of the stolon, which 

 becomes converted into a single row of salpae, so placed that the 

 dorsal surfaces of all of them are toward the base of the stolon, 

 their ventral surfaces towards its tip, their right and left sides 

 on its right and left respectively, their oral ends at its top. or 

 neural side, and their aboral ends at its bottom, or genital side." 



"The single row of salpae becomes converted into a double 

 row, which consists of a series of right-handed salpae and a 

 sti i.s of left-handed ones, placed with their dorsal surfaces out. 

 their ventral surfaces towards the ventral surfaces of those in the 

 opposite row, and the left sides of those on the right and the right 

 sides of those on the left towards the base of the stolon. ' ' 



"In order to illustrate these secondary changes of position 

 let us represent the series of salpae by a file of soldiers, all facing 

 the same way. Now imagine that each alternate soldier moves 

 to the right, and the others to the left to form two files still 



ia The italics are mine. M. E. J. 



