No. I.] 



GAR-PIKE AND STURGEON. 



irregular corners of the blastomeres, and below the animal pole 

 it has extended deep into the germ-disc. 



The tJiird furrow, PI. Ill, Figs. 38 and 39, is of interest on 

 account of its irregular appearance : although usually vertical,^ 

 parallel to the first plane of cleavage, it may be meridional and 

 even strictly horizontal, with a range of intermediate variations. 

 As a large proportion (about fifty per cent) of the eggs examined 

 conformed to the plan of cleavage of Lepidosteus the writer 

 believes that this is the normal mode of cleavage of sturio. 

 It is first expressed, like the second cleavage, in the immediate 

 region of the animal pole, thence extends both centrad and 

 peripherad, but does not pass the limits of the blastodisc. 



Fig. 4. 



Marginally, however, it may attain the bordering pigmented 

 zone. It is in general readily distinguishable from earlier fur- 

 rows : the first cleavage has by this time completed its circle at 

 the yolk-pole of the ^^^ while the second has passed downward 

 through the pigmented zone and is half surrounding the yolk 

 mass. The niveau of the nuclei and the general pigmentation do 

 not differ from the earlier conditions. A horizontal section, 

 PI. IV, Fig. 57, may be compared with that of the eight-celled 

 stage of Lepidosteus, PI. II, Fig. 24. It will be noted that 

 in Acipenser the pigment has penetrated the first and second 



^ The observations were made upon eggs taken from a tray of which about 

 90% of the remaining eggs was successfully hatched. 



