362 
MESSRS. F. M. BALFOUR AND W. N. PARKER ON THE 
shoal at all according with their ideas of spawning beds. They remained hut 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 (1) an outer covering 
formed of elongated, highly refractive bodies, somewhat pyriform at their outer 
ends (Plate 21, fig. 17, fe.), which are probably metamorphosed follicular cells,* 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 (z.r.), and an inner and 
narrow homogeneous zone ( z.f .). 
Segmentation .—We have observed several stages in the segmentation, which show 
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 showed a vertical furrow at the upper or animal pole, extending 
through about one-fifth of the circumference (Plate 21, fig. 1), and in a slightly later 
stage we found a second similar furrow at right angles to the first (Plate 21, fig. 2). We 
have not been fortunate enough to observe the next phases of the segmentation, but 
on the second day after impregnation (Plate 21, 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- 
sac, is divided by a few vertical furrows, four of which nearly meet at the pole 
opposite the blastoderm (Plate 21, 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. 
Development of the embryo .—We have not been able to work out the stages 
immediately following the segmentation, owing to want of material; and in the next 
stage satisfactorily observed, on the third day after impregnation, the body of the 
embryo is distinctly differentiated. The lower pole of the ovum is then formed of a 
mass in which no traces of the previous segments or segmentation furrows could any 
longer be detected. 
Some of the dates of the specimens sent to us appear to have been transposed ; so 
that our statements as to ages must only be taken as approximately correct. 
Third day after impregnation.■ —In this stage the embryo is about 3‘5 millims. in 
length, and has a somewhat dumb-bell shaped outline (Plate 21, fig. 5). It consists 
* 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 anything 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. 
