NO. 1431. . BREEDING HABITS AND EGG OF PIPEFISH— GUDGER. 489 



Thus the segmentation cavity has been enlarged and the cells are more 

 scattered than in the preceding. The cells are grouped in twos, 

 threes, and fours. The thick periblast has several nuclei in the rest- 

 ing condition. There is a well defined '"epidermic stratum," as the 

 English writers term the outer layer of cells. 



Fig. 79 represents the last type of this stage, and need detain us 

 but for a few moments. Its outer cells are flattened and unequal in 

 size, and the interior cells are the largest of all. The periblast is very 

 thick, 3'olky, and indented from below by large vacuoles. On the 

 left a large cell has been cut out of the ''^Rmid^'' and at the right a cell 

 indents the perildast, while in the center cells seem to be in process 

 of formation from the basal layer. This blastoderm is closelv related 

 to that illustrated in section by tig. 74. 



Fio-. SO is a horizontal section through some such blastoderm as 

 that illustrated in vertical section in tig. 78, Plate X. It shows the 

 loose arrangement of the interior cells, and the drawn out cells of the 

 '''Dccl'incJiicht."' This was broken at several points in the process of 

 sectioning. 



L.\TEST STAGES OF SEGMENTATION. 



From this time on it is not profitable and is hardly possible to 

 follow the segmentation, but some figures may be introduced to show 

 the course of development. 



Fig. SI, Plate XI, is probably a descendant of a form like fig. 70, 

 Plate X. There is an '' eindermic stratum,*" the cells are loosely 

 scattered in the large segmentation cavity. The periblast is quite dis- 

 tinct, free from yolk, and has a good many nuclei. Just across the 

 border from one of these nuclei is a cell, in another place a cell lies in 

 a depression in the periblast. 



Fig. 82 is another type with '''Decksc/iic/tt^"' with cells fairly closel}^ 

 crowded in the segmentation cavit}^, and with a very thin periblast 

 out of which cells are being budded or into which they lose them- 

 .selves. At one or two places the periblast is reduced to the thickness 

 of a cell wall, and in neigh])oring sections nuclei abound in it. In the 

 left outer periblast two tripolar spindles are found. These have been 

 noticed occasionally in other sections. 



Fig. 83 is the typical Teleost late lens-shaped blastoderm. It closely 

 resembles Fusari's (1890) fig. 9 for C?'isticeps, and is almost a duplicate 

 of Samassa's (1890) fig. 3 for the salmon in corresponding stages. 

 The depression of the blastoderm into the yolk is probably due to 

 pressure against the eggshell. In the highest part of the epidermic 

 stratum is a very large cell, and in the right '""Rand'''' a giant nucleus, 

 which is separated from the neighboring cell by hardly more than the 

 cell wall. At the left a cell has been cut out of the '''Rand.'''' The thin 

 periblast has resting on it many cells, neither the origin nor the fate 

 of which can safely be passed upon. 



