of the Fishery Board for Scotland. 



33 



Experiment 5. — Ova were taken from a living female and placed in a 

 beaker of water taken direct from the sea, so as to be sure it contained no 

 spermatozoa, there being no *herring in the neighbourhood of Rothesay 

 Bay at the time. Twenty-four hours afterwards all the eggs were still 

 unchanged. Tliere ivas no separation of the egg membrane from the yolk 

 in any of the ova. 



Experiment 6. — In this experiment the same ova were used as in 

 experiment 5. After remaining unchanged in sea water for twenty-four 

 hours they were mixed with living milt. A few hours afterwards a 

 breathing chamber was formed at one pole in nearly all the eggs, and the 

 egg capsule was thinned out at the opposite pole. There was, however, 

 no further development. 



Experiment 7. — In order to ascertain if active spermatozoa were to be 

 found in any of the tanks adjoining those in which the living herring 

 were kept, eggs were taken from a living female and placed in water from 

 an adjoining tank. Care was taken that no spermatozoa were introduced 

 during the experiment. Next day a small percentage of the eggs were 

 developing quite normally, but the majority remained unchanged. 



Experiment 8. — Ova from a female which had only been dead a short 

 time were mixed with milt from a male that had been dead three hours. 

 Next day a few of the ova were developing quite normally, but the 

 majority remained unchanged. 



The foregoing experiments appear to justify the following conclu- 

 sions : — 



1. The ova retain their vitality, and are capable of being fertilised 

 from forty to forty-eight hours after the female is dead. In the experi- 

 ments performed forty-eight hours seems to be a little outside the limit at 

 which the eggs are capable of being fertilised, but it is probable that 

 temperature may have an influence on the vitality of the ova. 



2. The spermatozoa do not retain their vitality for nearly so long a 

 period. Three hours appears to be the limit indicated by the above 

 experiments. 



3. The egg capsule never separates from the yolk excepting under the 

 influence of spermatozoa. It would appear that when the ova and 

 sf ermatozoa have partly lost their vitality a partial separation of the egg 

 membrane from the yolk may take place, although the ovum is not truly 

 fertilised. Experiment 5 shows conckisively that the egg capsule is not 

 permeable to water until after it has been penetrated by spermatozoa. 



4. The egg membrane is covered with a viscous secretion when the 

 ovum leaves the oviduct, which serves for the attachment of the ovum. 

 This viscous layer gradually hardens in sea-water. Active spermatozoa 

 are able to penetrate this layer some hours after it has set, but this power 

 appears to be confined to the first twenty-four hours after deposition. 



5. There is no collection of germinal protoplasm at the surface of the 

 yolk in the ripe ovarian ovum, nor is a germinal disc ever found so long- 

 as an ovum remains unfertilised. The formation of the germinal disc 

 cannot be made out in living ova, and its true nature can only be 

 determined from a study of sections. 



2. Formation of the Blastoderm. 



I have already summarised Kuptfer's conclusions on this subject in the 

 first part of this paper (Third Annual Report S.F.B., 1884). My obser- 

 vations do not coincide with his on many points, but the chief differences 

 are to be explained, I think, by the fact that Kupffer had not an 

 opportunity of examining sections in the earlier stages. In the ripe 



C 



