742 STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 



multitudes, on every shoal at all according with their ideas of 

 spawning beds. They remained but two days. During the 

 summer it happens now and then that one is seen to come up for 

 his mouthful of air ; beyond this there will be nothing to suggest 

 the ravenous masses hidden by the darkness of the waters." 



Egg membranes. The ova of Lepidosteus are spherical bodies 

 of about 3 millims. in diameter. They have a double investment 

 consisting of (i) an outer covering formed of elongated, highly 

 refractive bodies, somewhat pyriform at their outer ends (Plate 

 34, fig. 17, f.e.}, which are probably metamorphosed follicular 

 cells 1 , and (2) of an inner membrane, divided into two zones, 

 viz. : an outer and thicker zone, which is radially striated, and 

 constitutes the zona radiata (2. r.}, and an inner and narrow 

 homogeneous zone (z. r'.\ 



Segmentation. We have observed several stages in the seg- 

 mentation, which shew that it is complete, but that it approaches 

 the meroblastic type more nearly than in the case of any other 

 known holoblastic ovum. 



Our earliest stage shewed a vertical furrow at the upper or 

 animal pole, extending through about one-fifth of the circum- 

 ference (Plate 34, fig. i), and in a slightly later stage we found a 

 second similar furrow at right angles to the first (Plate 34, fig. 2). 

 We have not been fortunate enough to observe the next phases 

 of the segmentation, but on the second day after impregnation 

 (Plate 34, fig. 3), the animal pole is completely divided into small 

 segments, which form a disc, homologous to the blastoderm of 

 meroblastic ova ; while the vegetative pole, which subsequently 

 forms a large yolk-sack, is divided by a few vertical furrows, four 

 of which nearly meet at the pole opposite the blastoderm (Plate 

 34, fig. 4). The majority of the vertical furrows extend only a 

 short way from the edge of the small spheres, and are partially 

 intercepted by imperfect equatorial furrows. 



1 We have examined the structure of the ovarian ova in order to throw light on 

 the nature of these peculiar pyriform bodies. Unfortunately, the ovaries of our adult 

 examples of Lepidosteus were so badly preserved, that we could not ascertain any- 

 thing on this subject. The ripe ova in the ovary have an investment of pyriform 

 bodies similar to those of the just laid ova. With reference to the structure of the 

 ovarian ova we may state that the germinal vesicles are provided with numerous 

 nucleoli arranged in close proximity with the membrane of the vesicle. 



