No. I.] GAR-PIKE AND STURGEON. 15 



II. The Early Development of Lepidosteus. 



The Q^'g after being deposited becomes pale cream yellow in 

 color, and for a short time does not exhibit the protoplasmic 

 germ area. The condition of its membranes has been made 

 the subject of the exhaustive research of Mark, who figures 

 and describes for the first time the single micropyle and its 

 contained plug of granulosa cells. The maturation of the ^%g 

 has not been sufficiently followed by the writer to warrant dis- 

 cussion ; he notes that the Q.g% at the moment of extrusion 

 shows a well-marked maturation spindle in the immediate 

 neighborhood of the micropyle, of which Mark has given an 

 excellent figure ; a polar body is here given off almost imme- 

 diately after fertilization ; its appearance is similar to that fig- 

 ured by Bohm ^ in trout ; it has not, however, like the latter, 

 been seen to undergo a second division. 



The change in the egg-substance which permits the heavier 

 yolk to sink to the lower pole of the ^gg is not apparent to the 

 eye during the first ten minutes after fertilization ; the lower 

 hemisphere is then noted to be of a darker color. Soon after- 

 ward the ^gg presents somewhat the appearance of PI. I, Fig. 

 I, — its germ area, however, is somewhat larger than figured 

 and its marginal limit less clearly marked. The ^gg one hour 

 after fertilization, seen in the figure, is on the point of under- 

 going the first cleavage : its germ area is roundly oblong, of 

 flattened surface, slightly raised above the yolk. Sections, how- 

 ever, indicate that at this stage germ disk and yolk are more 

 intimately connected, and in PI. II, Fig. 21, it will be seen 

 that the protoplasm of the animal pole is hardly to be sepa- 

 rated from the coarse granular yolk until nearly in the equato- 

 rial region of the ^gg. In the figure the nucleus is seen dividing 

 at about one third the diameter of the ^gg from the surface. 



Segmentation. 



First Cleavage (PI. I, Fig. 2). — The first segmentation fur- 

 row appears in the living ^gg as a thinning away of the germ 



1 A. A. Bbhm: Die Befruchtung des Forelleneies. Sitz.-Ber.d. Gesell. f. Morph, 

 u. Physiol. Miinchen. 5 Mai, 1S91. 



