29G SEA-SIDE STUDIES. 



produces eggs, and not Medusae ; the other ^Medusae, and not 

 eggs. The same great anatomist assured me that he also had 

 seen something like what I have seen ; he had seen the 

 same species of Gampanularia producing both eggs and 

 MedusiT, " but no one believed me/' he added. The plea 

 for scepticism being, that Professor Kolliker must have 

 mistaken two different species for the same species — a 

 hazardous assertion, considering who is the observer. But 

 this objection cannot apply to my observation, for it was 

 on the same Polypidom that I found some of the capsules 

 filled with eggs, and some with Medusse. Even more start- 

 ling is the fact now to be mentioned. In one and the same 

 species {Myriophyllum), di'edged at the same time and from 

 the same place, I found the capsules containing eggs and 

 also Medusce ; and others — but not on the same Polypidom 

 — containing eggs and Polypes, i. e. the ciliated gemmules 

 which we knoAV to be the infusorial stage of the Polype. 



I have seen this so often that the whole history of evolu- 

 tion thus presents itself : Taking the medullary substance 

 of the Polype as the analogue of the cellular basis of the 

 plant, we may trace a somewhat similar course of evolution 

 in each : the cellular basis becomes differentiated into leaves, 

 stamens, pistils, germ-cells, and sperm-cells ; the medullary 

 substance becomes differentiated into nucleated cells — these 

 cells into germ-cells and sperm-cells, or into germ-cells 

 alone, from which are developed, 



1st, Under one set of conditions, probably of temperature 

 and food, Polypes ; 



2(1, Under another set of conditions, Medusje. Just as a 



