274 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



top of the figure some of these elongated nuclei are shown in various 

 stages of division. These are found in every section, and at a later stage, 

 Fig. 3, almost every nucleus is dividing, or is about to divide, or has just 

 divided, and the visceral nuclei thus show a marked arrangement in 

 pairs. 



The energetic multiplication takes place by direct division, and as it 

 goes on the chromatin is gradually exhausted, and the nuclei become 

 more and more transparent and vesicular, as will be seen by comparing 

 Figs. 1, 2, 3, 4, 5, 6 and 7, 8 of Plate XLII. At the stage shown in Figs. 

 1 and 2, the division takes place in planes concentric with the outer 

 surface of the embryo, or at right angles to the radii and to the long 

 axes of the nuclei, so that each nucleus falls, after the division, into a 

 peripheral and a central portion, lying in the same radius. 



The outlines of the visceral follicle cells, at this time and later, are 

 so obscure that it is difficult to decide whether the division of the nuclei 

 is, or is not, accompanied by cell division. Such cell boundaries as are 

 visible are always radial, as Figs. 2 and 5 show, and I have found no 

 trace of cell division in the planes of nuclear division, and it seems 

 probable that nuclear division goes on more rapidly than, or perhaps 

 without, cell division, so that each cell soon becomes polynuclear. 



Salensky shows four of these pear-shaped nuclei, with a deeply 

 stained area at the small end, in an embryo of Salpa democratica, near 

 the top of his Taf . 27, Fig. 2, dt, but he does not figure them in any other 

 species, and I can find no account of them in the text. We cannot fail 

 to notice the resemblance between those shown in my Fig. 1, Plate XLII, 

 and the pear-shaped bodies with a deeply stained spot at the small end, 

 which are figured in pyrosoma by Salensky (15), especially in his Figs. 11, 

 12, 14 and 19, although he' does not regard them as nuclei, but as pear- 

 shaped follicle cells (Kalymmocytes), with the deeply stained nucleus at 

 the small end. However the case may be in pyrosoma, the pear-shaped 

 bodies in the embryo of Salpa hexagona are not cells, but follicular nuclei. 



The account I have given of the way in which the nuclei multiply 

 will show that the result of this process must be a migration inwards 

 towards the center. Those which move in lines which carry them to the 

 blastomeres push into the layer of protoplasm around the big spherical 

 blastodermic nuclei. In several sections I have found follicular nuclei 

 half imbedded in the protoplasm of the blastomeres, like the one which 

 is shown on the left side of the middle blastomere in Fig. 1 ; and nuclei 

 which retain their pear-like shape and the spot of deep color at the small 



