AUGUST WEI S MANN 355 



suppose that, while four loops are sufficient to start nuclear division, 

 these loops must be of a certain size and quantity in order to com- 

 plete the whole ontogeny (in a certain species), it follows that eggs 

 possessing a reticulum which contains barely enough nuclear substance 

 to divide into four segments, would be able to produce the first divi- 

 sion and perhaps also the second and third, or some later divi- 

 sion, but that at a certain point during ontogeny, the nuclear sub- 

 stance would become insufficient, and development would be arrested. 

 This will occur in eggs which enter upon development without fertili- 

 zation, but are arrested before its completion. One might compare 

 this retardation leading to the final arrest of development, to a rail- 

 way train which is intended to meet a number of other trains at 

 various junctions, and which can only travel slowly because of some 

 defect in the engine. It will be a little behind time at the first junc- 

 tion, but it may just catch the train, and it may also catch the second 

 or even the third ; but it will be later at each successive junction, 

 and will finally arrive too late for a certain train; and after that it 

 will miss all the trains at the remaining junctions. The nuclear sub- 

 stance grows continuously during development, but the rate at which 

 it increases depends upon the nutritive conditions together with its 

 initial quantity. The nutritive changes during the development of an 

 egg depend upon the quantity of the cell-body which was present at 

 the outset, and which cannot be increased. If the quantity of the 

 nuclear substance is rather too small at the beginning, it will become 

 more and more insufficient in succeeding stages, as its growth becomes 

 less vigorous, and differs more from the standard it would have 

 reached if the original quantity had been normal. Consequently it 

 will gradually fall more and more short of the normal quantity, like 

 the train which arrives later and later at each successive junction, 

 because its engine, although with the full pressure of steam, is un- 

 able to attain the normal speed. 



It will be objected that four loops cannot be necessary for nuclear 

 division in Ascaris, since such division takes place in the formation 

 of the polar bodies, resulting in the appearance of the female pro- 

 nucleus with only two loops. But this fact only shows that the 

 quantity of nuclear substance necessary for the formation of four 

 loops is not necessary for all nuclear divisions ; it does not disprove the 

 assumption that such a quantity is required for the division of the 



