DEVELOPMENT OP THE SQUID. 5 



formed by separation, somewhat earlier, from the end of a pyramid. Inside this set is 

 another series, d!' , equal in number to the set d! , and arranged like this set, in pairs along 

 the radii which end in the pyramids. Inside there is another set d!" , of the same kind, so 

 that, as we pass inwards in the line of each pyramid continued, we have the following 

 series : 1, the pyramids ; 2, one large spherule, c ; 3, two spherules, d! ; 4, two spherules, 

 d!'; 5, two spherules, d!" . I was not able to trace the arrangement any farther on account 

 of the spherical shape of the egg, but the last series, d!" , was some distance from the 

 centre of the blastoderm, which appeared to be occupied by somewhat smaller spherules 

 than d!" . Although the earlier stages of segmentation were not observed, the phenomena 

 presented at this stage are sufl&cient to show that, as Lankester has stated (Observations 

 on the Development of the Cephalopoda), the egg of Loligo undergoes substantially the 

 same form of segmentation as that described by KoUiker in the case of Sepia. My 

 figures 1 and 2 obviously represent an egg a little older than Kolliker's figure 6, taf. 1, 

 (Entwickelungsgeschichte der Cephalopoden) as copied in Bronn's IQassen und 

 Ordnungen des Thierreichs, Band iii, taf cxxiii, fig. 13. Lankester states that the 

 segmentation is not as regular in Loligo as it is in Sepia, but the arrangement of the 

 spherules in our species seems to be perfectly regular, and the only important differences 

 from Sepia are the greater relative size of the nuclei, and the separation of the radiating 

 pyramids from each other by areas of unsegmented yolk, figure 2, a, a, a, in Loligo, 

 while the pyramids are almost in contact with each other in Kolliker's figures, as copied 

 by Bronn. 



In an optical section of the egg at this stage, the blastoderm, figure 2, c, is seen to be 

 formed of a single layer of large spherules, resting directly upon the yolk, d, from 

 which they are sharply separated in the centre, but less sharply at the edges. In the 

 species which Lankester studied, the blastoderm at about the same stage as our figure 1, 

 is several cells thick at its edge, (see Lankester's figure 1, x), but this is not the case in 

 our species. 



Figure 3 is a somewhat older egg in the same position as figure 1 ; a, is the egg shell ; 

 6, the space occupied by the albumen ; c, the blastoderm ; d, the yolk ; and m, the 

 micropyle as before. The blastoderm now covers a considerable area at the formative 

 pole of the egg, and its edge is marked by two parallel lines around the yolk. The 

 outermost of these lines appears to be the growing edge of the layer of ectoderm, 

 which has been formed by the subdivision and increase of the segmentation spherules of 

 an earlier stage, and the second or inner line I believe to be the growing edge of the 

 lower layer of the blastoderm. The surface of the yolk below the blastoderm and 

 inside this second line is covered by a number of large, weU-defined, nucleus-like bodies, 

 the autoplasts of Lankester, which are strictly confined to the area inside the inner 

 one of the two circular lines noticed, and in no case reach to or beyond the growing 

 edge of the blastoderm. The appearances indicate that these bodies are the nuclei of the 

 lower layer or endoderm, which is in process of formation on the surface of the yolk 

 under the outer layer or ectoderm, but covering a smaller area, so that the ectoderm 

 projects beyond the lower layer a little around the entire growing edge. 



According to Lankester's observations (page 39 and plate 4, fig. 1), the autoplasts 

 of the egg of Loligo cover the surface of the egg far beyond the growing edge of the 



