TRANSACTIONS OF SECTION D. 417 



urination in the ovary long before fertilisation. It was with the object of more 

 carefully investigating this matter that the present work was undertaken. 



The two kinds of eggs are laid together at the same time, as Korschelt has 

 determined, and in a few days the male egg gives rise to the rudimentary male, 

 which at the time it is ready to leave the egg capsule is fully grown and sexually 

 mature, while the female at the moment she leaves the capsule is small and 

 immature. As the young worms develop in the egg capsule they are seen to 

 spin round, and as the moment for hatching approaches they become very active. 

 Shortly before the female leaves the capsule, the small males are seen actively 

 copulating with them, so that each female when it leaves has already been 

 fertilised. 



This process can be easily observed under the low power of the microscope, 

 and the actual passage of the sperm from the testes of the male into the body 

 of the female witnessed in the living state. Each female is seen to carry a 

 small mass of active sperms on the ventral side of the gut, at the point of 

 junction of stomach and intestine. If sections are cut of the female at this 

 stage, it is seen that although the sperms are collected where the future ovary 

 and ova will appear, no trace of them can at this time be detected. The ova 

 first appear at a much later date, when the female has grown very considerably 

 in size. They are then seen as a few small nuclei, which grow rapidly. Shortly 

 after the female germ-cells appear it is seen that each one is joined by a 

 spermatozoon, the head of which has become embedded in, or attached to, its 

 nuclear wall, so that ultimately the nucleus of each primitive ovum is seen to be 

 composed of one part, derived from the spermatazoon and the other part of the 

 female portion. These two elements of the nucleus never fuse, but retain their 

 individuality throughout all the various oogonial divisions. The double nucleus 

 divides amitotically ; each half separately. In the majority of these divisions 

 the male and female portions of the nucleus divide equally, so that a similar 

 quantity of nuclear material, both male and female, goes into each daughter 

 cell. There are probably about forty to fifty oogonial divisions in all. In all 

 these the male and female portions of the nucleus divide and move apart 

 simultaneously. Now and again, however, the female half of the nucleus seems 

 to divide before the male portion, so that the male portion gets left behind and 

 is shut off entirely in one of the daughter cells. Therefore of the two resulting 

 daughter cells one has the whole of the male part of xhe original nucleus and 

 its share of the female portion, while the other has only its half of the female 

 and no male substance. This appeal's to be the sex determining factor; for of 

 these two daughter cells, the one that has received the whole of the male 

 element and the female element becomes the female, while that which has 

 received the female portion alone, becomes the male. Both these two kinds of 

 eggs, once the sex determining division has taken place, grow rapidly. They 

 seem to do this through the power of absorbing and building up into themselves 

 all the other immature egg cells with which they come in contact, and in which 

 the divisions of the two portions of the male and female substance have been 

 equal. The outcome of this process is that the male egg is not fertilised, while 

 the female egg is fertilised. It is, however, impossible to speak of the male egg 

 as unfertilised, as it has been directly under the influence of the sperm in all 

 the oogonial divisions previous to the sex determining one. It is only in the 

 late stages shortly before the egg is laid that the two parts of the nucleus fuse 

 beyond recognition. As the two kinds of eggs, male and female, are not found 

 in equal numbers, it is probable that one of them undergoes division in turn, 

 and I am inclined to believe that this is the female, as the female eggs are laid 

 in the proportion of three to one of the male. I have not decided this point. 

 The naturation divisions have been studies in both eggs, but I desire, to 

 withhold any statements with regard to them till I have studied them more 

 thoroughly. 



1911. 



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