W. K. BROOKS ON THE GENUS SALPA. 245 



to preface my account of my new observations by a short outline of 

 features which have already been so well described. 



The unfertilized egg in its follicle, Plate X, Fig. 1, lies in the body 

 cavity of the chain-salpa, where it is suspended from the wall of the 

 atrium by the fertilizing duct, which shortens after fertilization in such 

 a way as to draw the egg up to the point where the duct is attached to 

 the wall of the atrium. The way in which the egg reaches its final posi- 

 tion by the shortening of the suspensorium has been well described in 

 minute detail by Leuckart (1), p. 48 ; by Salensky (5), pp. 183-5, and by 

 Barrois (4). 



While this change is taking place the embryo begins to grow and to 

 project into the atrium, pushing its wall inwards as shown in Plate IX, 

 where 6, colored red, is the wall of the atrium, while the yellow tint 

 marks the body cavity. 



The embryo, in its follicle, colored blue, is then folded into an 

 epithelial capsule, which at first consists, like the wall of the atrium and 

 pharynx, of very flat cells, Plate X, Fig. 6, 6', colored red in the figures. 

 Soon the cells immediately around the point where the egg jis fastened, 

 Plate X, Fig. 9, 11, become thickened and columnar, Plate X, Fig. 9, &', 

 and thus become converted into the " Epithelhiigel " of Salensky. The 

 patch of thickened epithelium gradually spreads on all sides until it 

 ultimately covers the whole embryo, Plate XI, Figs. 1, 2 and 3, &', except 

 within the area which is shown in Fig. 3, between the 7 and the F of the 

 word Fig. This space never becomes covered by the capsule, and it 

 ultimately becomes the roof of the placenta, Plate XVIII, 10. As 

 regards the origin of the epithelial capsule, Salensky says (2), p. 182, 

 that it is nothing more than the thickening of the wall of the pharynx, 

 but this is certainly an error, although of little significance. The egg is 

 not fastened to the wall of the pharynx, but to that of the atrium. As I 

 did not reach conclusive proof of this error until after my drawing had 

 been finished for photolithography, I have used the colors and reference 

 letters for the atrium in these figures which are used elsewhere in this 

 memoir for the pharynx. 



It is possible that the epithelial capsule may be part of the wall of 

 the atrium, but I have already given my reasons, page 236, for believing 

 that the suspensorium, Plate X, Fig. 9, 11, may, while shortening, pos- 

 sibly spread out at its mouth and give rise to the area of thickened 

 epithelium, 6'. If this be the case, the epithelial capsule is follicular 

 in its ultimate origin. 



