W. K. BROOKS ON THE GENUS SALPA. 239 



side of the egg, wedged in between it and the follicle, is a small cell, 13, 

 which is probably a pole cell. 



The next egg which I found is in the eight-celled stage, and it is 

 shown in Plate IX, Figs. 1 to 10. The sections are transverse to the 

 oviduct and they begin on the proximal side, so that Fig. 1 is proximal 

 and Fig. 10 distal, and the small cell with the deeply stained nucleus in 

 the center of Fig. 1 is probably a pole cell. 



It will be seen from the figures that the eight cells are symmetrically 

 arranged in two sets of four each on the sides of a plane of bilateral 

 symmetry, which is also the plane which, at an earlier stage, passed 

 through the spermatozoon and the nucleus. 



The eight cells are wedge-shaped, and they are crowded together in 

 such a way that the broad ends of four of them, 1 and 2, and the narrow 

 ends of the others, 3 and 4, are proximal. Two of them, the upper ones 

 in the figures, are much smaller than the other six, which are nearly 

 equal in size. The nuclei of all of them are in a condition of preparation 

 for the next division, which will result in the formation of sixteen cells. 

 Two of the cells, 3 in Figs. 6 and 7, are more advanced than the other six, 

 and their nuclear figures show that the next division takes place parallel 

 to the second cleavage plane. 



The next stage which I have found is shown in Figs. 4 and 5 of 

 Plate X, cut nearly, but not exactly, in the plane of Fig. 3. There are 

 about sixteen cells, but as the planes do not coincide I was not able to 

 trace the exact relation between them and those of the eight-celled stage. 



The next stage which I have found is shown in Figs. 7 and 8. The 

 plane of the sections is longitudinal, or essentially like Figs. 3 and 5. 

 The blastomeres are now quite numerous, and they differ greatly in size, 

 and as they are now separated from each other by the mass of migrating 

 follicle cells among which they are imbedded, it is almost impossible to 

 trace the history and fate or the exact mode of origin of each cell, at 

 least by sections of preserved specimens, although more might possibly 

 be made out by the observation of living eggs during segmentation. 



Still older embryos are shown in Plate X, Fig. 9, and in Plate XI, 

 Figs. 1 and 2. The blastomeres which are now scattered throughout the 

 mass of follicle cells are not arranged in any discoverable order. Their 

 nuclei still continue to exhibit indications of division, and the protoplasm 

 of each blastomere now contains, besides the nucleus, a number of faintly 

 defined bodies, which I regard as the degenerating nuclei of the follicle 

 cells. 



