NO. 1431. BREEDING HABITS AND EGG OF PIPEFISH— GUDGER. 491 



modes of its formation in other Teleosts, and to show under which of 

 these cksses the pipefish egg falls, and finally to giv^e references to a 

 few of the more valuable papers on this subject. 



In Teleosts the periblast layer seems to be formed after three types: 



(1). In eggs, in which the tirst furrow cuts through to the yolk, the 

 periblast is formed by a thin protoplasmic sheet extending inward 

 from the '"'' Band.^' Henneguy (18S8, lig. 63) shows this very plainly 

 for the trout. 



(2). In eggs, in which there is no layei" of oil drops under the germ- 

 disk, or those in whicli the protoplasmic mass separates sharply from 

 the yolk, the periblast is formed when the inner ends of the cells in 

 the four and eight celled stages are cut out and lifted from the under- 

 lying thin protoplasmic sheet. This is the mode of formation in Ser- 

 ranus (Wilson, 1801), Ctenolabrus (Agassiz and Whitman, 1885), and 

 Belone (Kopsch, 19U1). 



(3). In eggs in which there is an imperfect separation of germ disk 

 and yolk, or in which there is a layer of oil drops under the blasto- 

 disk, the central periblast has a very peculiar mode of origin. Cells 

 are cut out of the protoplasmic disk in successive layers from above 

 downward and the central periblast is the renmant of blastodisk left 

 when this process has ended. The explanation for this is that the 

 protoplasm continues to flow out of the yolk into the germ disk until 

 segmentation has progressed some distance. Kupfl'er (1868) noticed 

 that the germ disk was not fully formed in a European Syngnathus 

 until after the four- celled stage. This formation for the central peri- 

 blast is described by most workers on the Salmonoids, notably by 

 Zeigler (1882), and Hoflmann (1888), for the salmon, and latest of all 

 by His (1898) for the salmon and trout. Kowalewski (1886) found 

 essentially the same formation in Cdrassius and I*(//(/acanthit.s. 



The central periblast nuclei, in types 1 and 2, originate by divi- 

 sion of the ''Rand'''' nuclei and migrate centralwards in this layer. 

 In Type 3 they are the direct descendants of the segmentation 

 cells. 



In Sijdio.sfo/ita forldpe there are found the two methods of central 

 periblast formation described in Types 2 and 3 above. In figs. 10, 

 45, 46, 47, 48, and 52 for the eight and sixteen-celled stages, there is 

 shown a mode of formation for the periblast which negatives the 

 idea that from it there could ever come any ""after-segmentation." 

 On the other hand, in figs. 53, 54, 55, 68, 59, 60, 61, and 62, the central 

 periblast is the protoplasmic remnant of the primary germ disk, left 

 after all the blastoderm cells have been cut out of it. It is well to 

 note here that a migration of nuclei into the marginal region and the 

 formation of a "wreath" by the disappearance of cell walls has, 

 because of the opacity of the Qg^^ not been seen in the pipefish. 

 Whether it takes place or not I can not say. 



