62 



microscope has revealed the fact that for some short period 

 (probably not more than a minute) after the extrusion of each 

 ovum from the female, there is a free communication from 

 the surrounding fluid, through one or more minute apertures 

 in the horny covering of the egg, to the germ in its interior. 

 The milt consists of myriads of wriggling spermatozoa, animal- 

 cules so minute as to require a microscope of very high power 

 to distinguish them ; during the short period that the com- 

 munication through the ovum of which I have spoken lasts, if 

 one of these myriads of spermatozoa finds its way into the 

 interior of the ovum the communication with the outer fluid 

 at once ceases, the ovum is fecundated and the growth of the 

 embryo commences. If, on the other hand, the ovum passes 

 through the period during which the communication with the 

 surrounding fluid lasts without coming in contact with any 

 of the spermatozoa the egg can never be fecundated, and can 

 never produce a fish, but remains for a great length of time 

 beautifully translucent, and apparently healthy. In a state of 

 nature large numbers of these uufecundated eggs are often 

 found, and it is but reasonable to suppose, therefore, that in 

 the natural deposition of spawn, many eggs escape contact 

 with the milt or germinating fluid. 



In the process of artificial fecundation the eggs and milt are 

 expressed into a vessel of water, mingled for a few seconds, 

 and then the surrounding fluid containing the excess of milt 

 is washed off. Of course, there is but little fear in this case 

 of any of the eggs escaping contact with the spermatozoa, and, 

 in fact, in the hands of skilled manipulators, few eggs fail. 

 Occasionally, however^ a whole batch fails, thus, amongst our 

 first successM shipment, no less than from 15,000 to 16,000 

 eggs, at first apparently the most healthy of all, had never 

 been fecundated, and were of course useless. In this ship- 

 ment about 10,000 must be placed in the same category. The 

 eggs of the female and the milt of the male may each be 

 expressed by a slight extra force, though not quite ready for 

 natural extrusion, and in either case (both of which are likely 

 to happen in comparatively inexperienced hands) I have no 

 doubt every egg would fail. Another cause of failure might 

 be the leaving the eggs a few moments too long before the 

 admixture of the milt ; many other causes may operate towards 

 the same end of which, in our present state of knowledge, we 

 are entirely ignorant, but I think I have said enough to con- 

 vince you that so far from the discrepancy referred to being 

 surprising, the wonder is that so large a number of fry may 

 be looked upon as comparatively out of danger. 



We must first reduce the rough estimate of 45,000 eggs 

 (which I still believe was under the true number) by 10,000 



