06 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



are shown at a younger stage in Plate XXIII, Fig. 10, which is just a 

 little above the level of Fig. 9. In Fig. 9 the pockets, 28, open into the 

 cavity, d', of the endodermal tube, while in Fig. 10, 28, they are closed, 

 and separated by the upper blood space, j, from the wall, d", of the endo- 

 dermal tube, d'. 



These blind pouches grow rapidly and soon reach the top of the 

 stolon, as is shown in cut N. ajid their slightly dilated oral ends, 27, o 

 and 28, o, lie at the sides of the ganglion, s, a"s is also shown in section in 

 Plate XXIV, Fig. 5, 27, 28 and s. This figure is the uppermost of the 

 series shown in Plates XXIII and XXIV, and in these plates, as well as 

 in those which follow, the capital letters A- A', B-B', etc., indicate the 

 same individual in the series of sections on Plates XXV-XXXIII, the 

 capital letter without an accent marking its right side, and the one with 

 an accent its left side. A-A' is the youngest and most proximal salpa, 

 B-B' the next, and so on to N-N', which is the oldest and most distal 

 one shown in these plates. A-A', C-O, F-F', H-H', J-J', L-L' and N-N' 

 are right-hand salpse, and the alternate ones are left-hand salpae. As the 

 body of an older salpa is longer than that of a younger one, it is cut by 

 more sections, and is shown in more figures. 



In all the figures 27 is the right half of the branchial sac, and 28 its 

 left side. It will be seen from the series of sections in Plate XXIV that 

 the upper or oral ends of the halves of the branchial sac, Fig. 5, 27 and 

 28, are dilated, and that, as we follow them down, Fig. 4, they become 

 smaller, until they enlarge again at the level of the endodermal tube, 

 Fig. 2, d', into which they open. Below the level of the endodermal 

 tube they run down for a short distance as closed tubes, Fig. 1, C, and 

 these tubes soon lengthen, like the oral ones, and become so long that 

 they reach the genital surface of the stolon ; but before this stage the 

 bodies of the salpae begin to push out of the line of the stolon towards 

 the right and left alternately, and they also begin to rotate on their own 

 axes. The omission of all reference at present to these secondary 

 changes will simplify the description so much that I shall from this 

 point on describe the development of the chain-salpa as if these changes 

 did not occur, and I shall illustrate it by imaginary diagrams. We shall 

 then be the better fitted for going over the subject a second time, as it is 

 actually exhibited in nature, and as it is illustrated by the figures of real 

 sections. 



Cut represents a proximal or dorsal view of a single salpa at the 

 stage just described, in which the endodermal pouches have reached the 



