76 S7MB10&ENESIS 



comparatively recent origin and those inherited from remote 

 ancestors. The "remote ancestor" has constantly played the 

 role of deus ex machind in the theory of evolution. For an 

 account of the essential endowments of a species, or an order, 

 or even of a whole class, we are generally referred back to a 

 common progenitor without any explanation of how he may 

 have come into being. Speaking of the advent of the mammary 

 glands, reference to which was made in the previous chapter, 

 Darwin tells us that they must have been developed at an 

 extremely early period, " and we can know nothing positively 

 about their manner of development." He also frequently 

 refers to "our ignorance of the past history of each species." 



My contention is that all species, strenuous and progres- 

 sive, or indolent and degenerate, can be traced back to a 

 strenuous remote ancestor, which arose symbiogenetically, i.e., 

 through protracted bio-economically useful association of 

 (bio-economically and physiologically) useful units. The 

 stored-up results of such symbiogenetic working associations 

 are the sine qua non of subsequent evolution, be it progressive 

 or retrogressive. 



In a degenerate we have frequently only rudiments left 

 indicating a once truly useful purpose, and their origins and 

 histories are usually overlaid by a plurality of perplexing 

 adventitious "characters" correlated with anti-symbiotic and 

 degenerate purposes, rendering it frequently extremely difficult 

 to sift the grain of usefulness left from the chaff of uselessness 

 superposed thereon. The usually very conspicuous adventi- 

 tious "characters" associated and correlated as they are with 

 morbid habits contracted at some time by an indulgent progeny 

 are thus in the majority of cases apt to mislead us as regards 

 the true character of the strenuous forbear. 



We have seen how the Convoluta are conspicuous and 

 remarkable among the Turbellarian worms in possessing no 

 excretory system, and we have set this retrogression down to 

 a parasitic diathesis. They are unlike their allies in this 

 respect, and the evidence seems to point to the fact that their 



