CYTOLOGICAL PROBLEMS 'jj 



is increased, so rendering possible the commencement of 

 segmentation. Working on frog eggs, he found that, after 

 pricking, the second polar body was given off, leaving the 

 nucleus haploid. Nuclear division then occurred, which in 

 all cases was not followed by cytoplasmic segmentation. After two 

 or three such divisions, the egg became polynuclear and died. 

 If, however, a little blood was introduced at the time of pricking 

 normal segmentation ensued. Bataillon had also made this 

 discovery, but concluded that the introduced leucocytes acted 

 as catalysers. Herlant, however, finding that around each 

 leucocyte a small aster developed, pointed out that by these 

 asters the volume of the cytoplasm, over which the spindle 

 had to take control before cell-division could occur, was reduced. 

 From such experiments he was led to the view that whenever 

 the nucleus is a " monocaryon " (haploid) the intervention of 

 a second factor, after that causing activation, is necessary for 

 development ; but when the nucleus is an " amphicaryon " 

 (diploid) a second factor is not requisite. Thus, in the frog's 

 egg simply pricked, without the introduction of blood, the 

 spindle becomes deeply implanted in the midst of an enormous 

 " female energid " (centrosome), and is incapable of controlling 

 effective segmentation. But in the egg pricked and treated 

 with blood or lymph, the accessory asters (energids) so produced 

 set up a dynamic change in the egg-cytoplasm rendering normal 

 segmentation possible. Therefore, " in fertilisation the male 

 pro-nucleus (apart from heredity) plays an important role by 

 its union with the female pro-nucleus ; for it re-establishes the 

 normal relation between the nuclear mass and the volume of 

 the ^gg." It will be noticed that Herlant's views are very 

 similar to those put forward by Hertwig, and generalised in 

 the well-known expression " Kermplasmarelation." 



Finally, a few facts put forward by Herlant in support of 

 his theory may be cited. It is well known that the egg of the 

 sea-urchin requires two factors to bring about development, 

 and correlated with this the egg-nucleus is a monocaryon, 

 due to maturation having taken place before treatment. 



In the starfish, on the other hand, maturation occurs after 

 the egg is laid, and it is possible for the experimenter to treat 

 such eggs either before or after the reduction division. Delage 

 found that treatment with the second agent could be omitted, 

 provided that maturation had not taken place (nucleus diploid) ; 

 if, however, the treatment was delayed until the nucleus was a 

 monocaryon (haploid) then the second factor was necessary. 



Again, in those cases where an egg is activated by foreign 

 spermatozoa the general principle appears to hold. Thus, in 

 the sea-urchin egg, activated by Mytilus sperm, the male 

 nucleus takes no part in mitosis. The egg-nucleus is therefore 



