324 SCIENCE PROGRESS. 



assumed archaic character of the former rests on any surer 

 basis than our inherent tendency to attempt to derive the 

 complex from the simpler forms of life. 



The outward semblance of the protoplastid body to the 

 metaplastid cell is the somewhat insecure footing on which 

 the cell theory set out to work its way into the complete as- 

 cendency it enjoys to-day, and unless some of our most funda- 

 mental conceptions of the relationships between living forms 

 are a delusion and a snare, there must exist somewhere be- 

 neath this outward semblance, a real community of structure 

 which it is not unreasonable to expect that our enormously 

 improved methods of investigation will suffice to show. In 

 reality so much that is entirely new and strange has been 

 lately added to our knowledge of the structure and life his- 

 tory of the protoplastids, and to the nature of the cyclical evo- 

 lutions among the metaplastid cells, that it is by no means 

 easy to say off-hand whether the cell theory has been weak- 

 ened or supported by it all. The value of recent work in 

 this direction may be perhaps best tested by the solutions it 

 can be made to offer of the two great problems which have 

 hitherto confronted the inquirers into the relation of the 

 protoplastid body to the metaplastid cell, and these pro- 

 blems may be stated thus : — 



i. There are forms of protoplastid which correspond in 

 gross to the components of a metaplastid cell. Is the 

 nuclear element in the former equivalent to the nuclear 

 element in the latter ? 



2. The conjugating Infusoria, during their multiplication, 

 go through a cyclical metamorphosis, and return at length 

 to forms similar to those from which they started. Is there 

 any evolution comparable to this in the successive develop- 

 ment of metaplastid cells ? 



I shall discuss the bearing of recent work on these two 

 questions in succession. As is well known, the nuclear 

 element in many Rhizopods is a large round body, having 

 about the same dimensions, relatively to the whole animal, 

 that the nucleus of a metaplastid bears to the cell in which 

 it is contained. According to the work of Gruber (i) and 

 others, the nucleus in Amoeba may become divided up into 



