SECT. 5] IN ONTOGENESIS 809 



being almost absent, and a delay in cleavage not exceeding 15 

 minutes occurred. From 30 to 55 atmospheres there was a critical 

 zone ; the percentage of eggs achieving complete first division rapidly 

 diminished until it reached a figure between 5 and 10. From 55 

 to 100 atmospheres, the state of affairs changed, for now, not only 

 would cleavage not take place, but a great number of abnormal 

 and teratological forms appeared. Later experiments gave greater 

 regularity, and the same process was gone through for each of 

 the early stages, i.e. second cleavage, third cleavage, fourth cleavage, 

 etc. The result was that for all the stages averaged, it took an osmotic 

 pressure of 33 atmospheres to stop 10 per cent, of the eggs developing, 

 and 39 atmospheres to stop 90 per cent, of them. Therefore an osmotic 

 pressure of about 1 1 atmospheres more than that of sea water was 

 required to stop development. Vies & Dragoiu went on to calculate 

 the work done in elevating the osmotic pressure to this point, and 

 hence "the external osmotic work of cytoplasmic division", 



where W is the work, co and wq the normal and stoppage osmotic 

 pressures, and V and Vq the normal and stoppage egg-volumes. The 

 values for W fell with development in a straight line, as follows : 



Ergs 

 First cleavage ... ... ... 4'09 



Second cleavage ... ... 2-05 



' Third cleavage ... ... 0-85 



Fourth cleavage ... ... 0-29 



Vies & Dragoiu pointed out that the "travail d'arret" diminished 

 as the volume of the blastomere diminished, but also tended to 

 diminish when related to the volume of the egg as a whole. Chevroton 

 & Vies had previously accurately measured the volumes of the blasto- 

 meres, finding, for instance, that the two were not quite halves and 

 the four not quite quarters. The following figures were obtained: 



Volumes "Travail d'arret" 



(Chevroton & Vies) (Vies & Dragoiu) 

 ( X io-« c.c.) (ergs) 



Unfertilised egg ... ... ... 52-3 — 



Fertilised egg (membrane) 

 (egg only) ., 

 i blastomere 

 J blastomere 

 ^ blastomere 



109-0 — 



47-7 4-02 



17-3 1-66 



7-78 o-8i 



2-64 0-28 



Vies & Dragoiu also made a cytological examination of the material, 

 and plotted the time taken to produce a definite morphological event 

 such as formation of accessory aster, or "paquet chromatique". 



