HISTORY OF THE EGG PROM FERTILIZATION TO CLEAVAGE. 21 



such a supposition, and the appearances in the fresh-laid Ctenolabrus egg, 

 although not decisive so far as we have been able to learn, do not favor it. 

 It is to be remembered, however, that the perivitelline space arises after con- 

 tact with water, and that only a few minutes at the longest elapse before 

 the space becomes evident. It is safe to say that tbe time of its appear- 

 ance varies from a few seconds to a few minutes, and that there is at least a 

 variation of some seconds in the time taken by the spermatozoon to reach 

 the egg and pass tbe micropyle. In most of our experiments in artificial 

 fertilization, the eggs were first placed in water, and then tbe milt added 

 as soon as the handling of a previously selected male fish would permit, 

 A minute might pass before the spermatozoa reached the egg, and a 

 thin perivitelline space might arise in tliis time. Whether it would be 

 sufficient to allow a displacement of the micropyle, we cannot positively 

 say, but tbe probability seems to lie in this direction. 



In those fish eggs that have a blastodisc already formed before fertiliza- 

 tion, the micropyle is usually described as having a central position, and as 

 sinking to some depth into tbe egg. This condition has been seen by Mr. 

 Whitman in the egg of tbe white-fish of Japan (Salanx microdon), and it 

 has been observed by Ransom (No. 8) and Tbompson 15 in the egg of the 

 stickle-back This is the position in which the micropyle is supposed to 

 remain until the spermatozoon enters the egg. We have invariably found 

 the micropyle eccentric, and on this point our observations agree with those 

 of His. 16 His concludes that the micropyle maintains a fixed position only 

 until the egg passes into the water ; after which time it may be displaced. 

 Speaking of the salmon and trout, His remarks : " So wahrscheinlich es 

 namlich a priori erscbeinen mag, dass die Lage der Mikropyle zum Keim 

 eine fest geordnete sei, so zeigt dock die Erfahrung tin den iin Wasser Uegenden 

 Eiern, dass der Keim innerhalb do- Kapsel verschiebbar ist, indem er bei. wechseln- 

 der Stellung der Letstern jeweilen in die obere Halfte des Eies riicJd. Man kann 

 sonach durcb allmahliges Dreben des Eies den Keim in beliebige Stellung 

 zur Mikropyle bringen, man kann ibn unter dieser durchgleiten lassen, 

 oder ibn an den der Mikropyle entgegengesetzten Eipol verlegen. Bei 

 Eiern, welche, sei es befruchtet oder unbefrucbtet, einige Zeit im Wasser 

 lagen, babe ich audi, dem entsprecbend, die Mikropyle an sebr verschie- 

 denen Stellen liegen seben. Meistens allerdings fand sie sich in der obcrn 



15 Allen Thompson. Tlic Ovum. Todd's Cyclop., V , 1859 



10 Wilhelm Ilis. Dntersuclmugeu aber das Ki uud die Eientwickelung bei Knoclicnfischen, p. 4. 

 Leipzig, 1873. 



