130 TRANSACTIONS AND PROCEEDINGS OF THK [Sess. Lxvi. 



great researches reveal not so much the origin of the germ- 

 cells in these as their remarkable migrations. 



In saying the foregoing in face of the known facts 

 concerning Moina, the dipterous insects, etc., Weismann 

 defined not only his own standpoint towards the question, 

 but also that of most other zoologists. The exception 

 meets with no favour, until it ceases to be such, and adapts 

 itself to the rule. But " die Natur geht ihren Gang, und 

 was uns als Ausnahme erscheint ist in der Eegel." And 

 this is so, simply because what we regard as the rule is 

 often false, the real law being that with which the 

 apparent exception conforms. 



While only from two to eight primary germ-cells were 

 found very early in the development of this or the other 

 form ; while, as in the higher animals, one could study the 

 early development without seeing any germ-cells— their 

 " segmental origin " even being witnessed at later periods 

 — the good old rule, in plain language, the superstition, 

 that the offspring was formed by the union of a small 

 portion of each of its parents, seemed to be the only 

 logical conclusion. Thus it happened that so great an 

 investigator and thinker as Darwin could set up his 

 provisional hypothesis of pangenesis. 



When in one of the higher animals, the skate, the 

 formation of a whole battalion of germ-cells is found to 

 take place prior to the appearance of any trace of the 

 embryo, a change comes over the scene : the apparent law 

 and its exceptions exchange positions, with the consequent 

 disappearance of the former. 



In the life-cycle of the skate (including in this all that 

 happens from the union of egg and sperm, until new eggs 

 and sperms are formed) the origin of the germ-cells fills in 

 so large a space as to overshadow completely everything 

 else. For this reason the formation of an embryo may be 

 described as a mere incident in the life-cycle. 



Two primary germ-cells and five hundred and twelve 

 are very different numbers. If the full significance of this 

 should not be apparent, a glance at the diagrammatic 

 representation of the life-cycle of the skate may serve to 

 make it so. The diagram is, however, incorrect ! In the 

 portion showing the origin of the primary germ-cells, these 



