502 Causes and Course of Organic Evolution 



data as Balanoglossus and such Cephalochordata as Amphi- 

 o.Tiis are side derivatives from these of greatly higher organi- 

 zation, the cihated nemerteans exhibit so many and so detailed 

 points of morphological and physiological contact with the 

 cyclostomes that one can readily construct what has been 

 termed in this work a j^rotocyclostome form. This would 

 serve to connect higher nemerteans with a type pretty closely 

 related to the now scarce — generically — and somewhat degen- 

 erate examples of cyclostomes at present alive. The organic 

 gap now existing however is a wide one. From allies of the 

 cyclostomes, that are extensively ciliate in the larval state, 

 to allies of the xVpoda, the morphological continuity is again 

 l^ronounced, and from the latter to simpler urodeles, thence to 

 higher urodeles with ciliate larvse, the connecting chain is 

 surprisingly clear. (See "family tree," facing p. 474.) 



A wide organic gap in the evolving process, that is repre- 

 sented in geological time by the upper carboniferous and per- 

 niian epochs, again separates the higher urodeles from the 

 primitive marsupials. For the writer decidedly follows Huxley 

 in considering that the true pathway of advance to the primates 

 is to be sought for in batracho-marsupial and marsupio-mam- 

 malian affinities. Evidences therefore have been advanced 

 for connecting the marsupials as a primitive but plastic group 

 vnih the Lemuridse, at the same time that the fnarsuj^ials 

 served as the starting point for most of the mammalian fam- 

 ilies. The opinions of Haeckel and of Cope have been ac- 

 cepted, which advocated that extinct types of Lemuridse made 

 connection Tvdth the anthropoid apes, while the latter have 

 been accepted as being in a nearly direct line of ascent to man. 



Such a trend of evolutionary progress does away entirely 

 with the need for a marine ancestry at any stage in the process. 

 For, even though, in the case of some nemertean and cyclo- 

 stome features, our descri])tions have directly or tacitly per- 

 tained to semi-marine or marine forms, such strong evidences 

 exist of the original fresh-water origin of these, and of their 

 probable great abundance in such waters in past geologic 

 time, that we have used the existing marine types as accessory 

 collateral evidence only. 



