482 PROCEEDTNGS OF THE NATIONAL MllSEVM. vol. xxix. 



egg- in the l)hist()d(M-ni.s in question is equatorial or at least approaches 

 very close thereto, and it seems hardly going too far to say that such 

 pipefish blastoderms as tigs. 10, 11, 1-1, 18, 20, there? is a reversion to a 

 tj'pe of segmentation essentially like that of Amphibia. 



thirty-t\v(>-cellp:d stage. 



Normal types of this stage, as shown in tig. 23, Plate VI, were found 

 to make up about 30 per cent of one lot of eggs, and were noted spar- 

 ingh^ in all others. Fig. 23 is plainly a derivative of forms like figs. 

 1() and IT, and, while it may be called normal, is noticeably diti'erent 

 from Wilson's tigures of the same stage for Serranus (tigs. 6, 8, 9, 

 and 10). No section of this stage will be given. Its internal struc- 

 ture will l)e made clear by reference to tig. 40, Plate VII, a sixteen- 

 celled blastoderm ready to divide into thirty-two. The two central 

 cells will divide horizontally, the two lateral ones by an oblique plane 

 resulting in six surface and two interior cells. (Compare Wilson's 

 fig. 18.) 



Fig. 4tt, Plate VIII, is a section from a flat-topped abrupt-edged blas- 

 toderm, drawn with the same magnitication as the others. It serves 

 to show the inequalities in the size of the blastoderms. The peri- 

 pheral cells are very nuich flattened above, though retaining their 

 rounded forms ])elow. To the right the sectioji cuts the point of a 

 sixth cell. The segmentation cavity {s. c.) is partially fllled with 

 cells. The larger and lower cell seems to have been cut ofl' from the 

 central periblast {c. p.), from which it is separated by a cell wall so 

 delicate that the oil inunersion oidy will detect it. It is like the peri- 

 blast in that its periphery contains many yolk granules. 



Fig. 24, Plate VI, is an arched type, with the highest point rather 

 nearer the lower side. The twenty-seven outer cells are in three 

 tiers, and while the second is pretty" sharph" marked ofl' from the flrst 

 there is but little difi'erence in level between it and the third tier. 

 There is here noticeable a symmetry comparable to that in flgs. 7 and 

 8. The plane 1 — 1 in all probability represents the flrst, 2 — 2 the sec- 

 ond line of division referable to flg. 4. 



A central section through tig. 24 in the plane a — h is shown in flg. 

 50, Plate VIII. The peripheral cells form an arch with the highest 

 point slightly to one side, and inclose a segmentation cavity which is 

 almost filled with cells. The two smaller cells have been cut ofl' from 

 the yjeripheral ones, the larger probably from one of its fellows. The 

 periblast is thick and yolky. A more pronounced large-ended type 

 is fig. 51. Here the segmentation cavity is somew^hat eccentric, and, 

 as in the preceding, the thick end ovei'hangs the base. The spacious 

 segmentation cavity (.v. c.) contains one cell which abuts on a curious 

 tongue of protoplasm from a partially segmented region on the left. 



Fig, 25, Plate VI, is a typical high-piled blastoderm, whose cells are 



