W. K. BROOKS ON THE GENUS SALPA. 273 



the primitive digestive cavity, but lie agrees with me that their lining is 

 derived from the somatic layer of the follicle, and that it is used up as 

 food. 



SECTION 6. The Nutrition of the Blastomeres and the fate of that part of 

 the Visceral Ixiyer of the Follicle which penetrates betiveen the Blasto- 

 meres. 



We come now to a most interesting and remarkable feature in the 

 history of the salpa-embryo, the nutrition of the blastomeres; and we 

 are here brought into direct opposition to Salensky, for my view of the 

 fate of the follicle cells which push in among the blastomeres is totally 

 and fundamentally different from his, although even here the difference 

 is rather in the interpretation of the observations than in the observa- 

 tions themselves. 



I have already given, pages 25 and 26, a brief outline of the way in 

 which the blastomeres are nourished by the follicle cells, but the subject 

 is so important that I must now discuss it more minutely, although the 

 reader may find in a review of these pages a good introduction to the 

 following account. 



During the early stages in the migration of the follicle cells nuclear 

 figures are found occasionally in the visceral portion, as is shown in Plate 

 X, Fig. 9, but these soon disappear, and while the cells, or their nuclei at 

 least, continue to multiply with very great energy, this takes place by 

 direct division. Plate XLII, Fig. 1, is a greatly magnified drawing, 

 made under a Tolles i used as a homogeneous immersion objective 

 with a long tube and A eyepiece, of a section of an embryo of Salpa 

 hexagona in the series from which Plate XI, Fig. 1, was drawn. In 

 both figures, 7 is the somatic layer of the follicle ; 8 is the visceral layer, 

 and 9 the blastomeres. The somatic layer stains more deeply in haema- 

 toxylin than the visceral layer, and this is even more true of their nuclei, 

 although at this stage the visceral nuclei take more color than they do 

 at later stages. 



The most conspicuous peculiarity of the visceral nuclei is that they 

 are elongated in lines which are radial to the subspherical embryo. 

 They are irregularly pear-shaped, and in most of them the small end is 

 towards the center of the embryo. Even at this stage the amount of 

 chromatiri is less than it is in the somatic nuclei, and it is concentrated, 

 in a mass which stains very deeply, at the central pointed end. Near the 



