SYMBIOSIS 37 



himself with registering and emphasising the connection 

 between the alternations of "usual food" and "other fare" 

 and those of sex in the various instances of metamorphosis, be 

 they manifested by plantagen or by insect. As I have already 

 remarked, he has no explanation to offer. The connection 

 itself has already been pointed out by others, except that Mr. 

 Davidson's plantagen theory adds a valuable factor, hitherto 

 missing, towards the recognition of the underlying bio- 

 economic principles. We see now why Mr. Davidson was 

 driven to make his comparison of plantagens (in surfeit) with 

 lowly orders of insects, viz., for the reason already stated, 

 that he is there, where degeneration is of frequent occurrence, 

 in reality comparing similar phases of bio-economic 

 abnormality. 



The case of the more stable higher insects and of the 

 higher animals propagating chiefly sexually, like that of the 

 higher green plants, stands on a different level. 



There remains, as Prof. Keeble points out, a wide gap 

 between the state of affairs in C. roscoffensis and that in the 

 higher green plant. 



" Sooner or later, C. roscoffensis destroys and digests its 

 green cells, and none of them, nor any colourless representa- 

 tives of the green cells, pass into the egg-cells ; whereas the 

 higher green plants provide for the future crop of chloroplasts 

 in their descendants by transmitting colourless rudiments of 

 the chloroplasts to their egg-cells." 



The symbiosis between animal and plant partner in 

 C. roscoffensis is thus retrograde and unstable as compared 

 with the domestic symbiosis in the higher green plants, and 

 this chiefly because it fails in biological symbiosis ; neither 

 Convoluta nor rose-aphis can obtain any abiding gains, can 

 set up a permanent and mutually auspicious relation with the 

 plants they exploit, or produce any bio-economic values, i.e., 

 social or communal utilities, in virtue of this exploitation. 

 Both require renewal by fresh " blood," the blood formed in 

 dishonest living not being conducive to effective nutritional 



