144 John priestlett. 



such a work, to be taken up under the stimulus of present 

 developmental questions, could not fail to be of great use ; 

 and he accordingly commenced observations on the ova of 

 rabbits. The present small publication is the forerunner of 

 a larger memoir which is to contain numerous plates. 



According to Van Beneden's observations the germinal 

 vesicle of the rabbit's ovum includes a clear liquid which is 

 traversed by a granulous substance (nucleoplasma) often in 

 the form of a reticulum. In addition to this there exists a 

 nucleolus and a few round bodies called pseudo-nucleoli. 



As maturity approaches the germinal vesicle moves towards 

 the periphery of the ovum, which has become distinguishable 

 into cortical and medullary portions, and takes on an ellipsoid 

 form applying itself to the pellucid zone. A clear, non- 

 granular portion of the cortex then accumulates about the 

 germinal vesicle, forming Avhat Van Beneden calls la lentille 

 cicatriculaire. Meanwhile the nucleolus fuses with that 

 part of the vesicular membrane which is nearest the edge 

 of the ovum, and the membrane itself, becoming thinner, 

 gradually disappears. 



While this is taking place the nucleoplasma together with 

 the pseudo-nucleoli melt into a granular nucleoplasmatic 

 body, and the fluid contents of the germinal vesicle are ab- 

 sorbed into the cicatricular protoplasm. Simultaneously the 

 changed nucleolus, which, on fusion, had extended into a 

 plate, gathers itself together into an ellipsoidal or lenticular 

 micleolar body. By the time the vesicular membrane has 

 disappeared the cicatricular protoplasm, after infiltration by 

 the vesicular fluid contents, has become again granular and 

 indistinguishable from the surrounding cortical mass ; and 

 the vitellus commences to withdraw from contact with the 

 pellucid zone and to express into the space thus left a clear 

 perivitelline fluid. Into this perivitelline space the nucleo- 

 plasmatic and nucleolar bodies are expelled, forming the 

 Richtungsbldschen (Fritz Miiller) or globules polaires (Eobin) 

 of other observers. All distinction of cortex and medulla has by 

 this time vanished, and the yolk, at this stage, truly merits 

 the name Monerula (Haeckel). 



The ovum is now ready for fertilisation; all the steps 

 hitherto recorded taking place while the ovum is still 

 ovarial. 



The act of fertilisation is the passage of spermatozoids 

 through the zona pellucida, which Beneden is now convinced 

 presents no micropyle ; once in the perivitelline space, they 

 apply themselves by their heads firmly to the vitelline sphere, 

 without, however, in any case penetrating into its substance. 



