343 
or asexual generation. But for this reason, and but for the parallelism 
between the modes of segmentation and the ways in which the mero- 
cytes and yolk are disposed of in Amphibians, Ganoids, and Elasmo- 
branchs, there would be no occasion to speak of the segmentation 
here. Every little fact has its own importance, as was previously in- 
sisted, and, as often happens, its meaning may at times only become 
obvious in the light of other facts. If Dean were correct, the segment- 
ation in Lepidosteus would be to all extents and purposes that of 
Scyllium, whereas if the the view BALFOUR and PARKER and I took of it 
be the right one, it would form a link!) between that of a frog or 
newt on the one hand and that of a skate or dog-fish on the other. 
This being so, the question of fact becomes of some importance. 
Dean has certainly had good opportunities for making sure of the 
point and — my own have been equally good. So far as can be 
gathered from DrAn’s statements and from my own abundant material 
of this period of the development, the crux of the matter lies in the 
mode of preservation. DEAN appears to have made no use of osmic 
acid in his investigations. The only two reagents employed by me 
were FLEMMInG’s fluid and corrosive sublimate. 
Eggs preserved in the latter fluid show no signs of the eight fur- 
rows described by myself, unless any sublimate remaining in the super- 
ficial part of the egg be precipitated by some such reagent as baryta 
water, but all the eggs of the proper stage (Fig. 3 of BALFour and 
PARKER’s memoir) show either 4 or 8 complete furrows reaching to 
tho lower pole. It is so easy to see these furrows in eggs lying in 
alcohol, or in eggs passed through turpentine and then dried, that 
I have often demonstrated them to others. So much for the segment- 
ation, the bearings of the facts will be apparent at a later stage. 
As to the time of their first appearance, and as to the mode of 
development of the merocytes in Lepidosteus, no observations have as 
yet been made. They certainly arise at an early period and probably 
during the segmentation, and as certainly they cannot?) here be de- 
rived from supernumerary spermatozoa. 
By the time the embryo has attained a length of 8 millimetres, 
and the yolk plates in its cells — the bane of proper investigation of 
the earlier stages — have mostly been used up, the merocytes form 
a fairly even layer over and around the yolk. For a considerable 
1) Not necessarily of a genetic kind! 
2) Vide E. L. Marx, Studies on Lepidosteus. Pt. I. Bull. Mus. 
Comp. Zool., Vol. XIX, No. 1. 
