rived fron the entire absence of any indication of another 

 origin, almost amounts to a certainty that these cells are 

 truly mesodermal. 



If then this assumption be admitted, a discussion 

 of the nature of these cells and the part played by them 

 in the developing bud is not out of place. 



In the case of a fixed organ, like the ganglion or 

 pericardii.m, which has a definite and determined position, 

 the cells destined to form it, must by virtue of their motile 

 power come together at the right time and place. 



Weismann (35; pages 161-52) in discussing the pro- 

 cess of gemmation in Gla velin a, as described by Seeliger (29), 

 supposes that t.-ie nescdermal cells "contain very different 

 kinds of idioplasm: ox\p , for instance, might contain 'muscle 

 determinants', and another, 'nerve-determinants', and a third 

 •blood-corpuscle-determinants'." He further adds, that 

 "until we knov/ more of the actual facts concerned, we can on-' 

 ly -- ho\7ever unsatisfactory such an assumption may be -- at- 

 tribute to the cells a tendency to become attached at defi- 

 nite points according to the manner in which they have pre- 

 viously been determined." 



It seems to me, however, that the opposite assump- 

 tion, which Weismann regards as less likely, namely, "that 

 these cells develop into muscle, nerve, or sexual cells 

 according to their point of attachment," is more in accor- 

 dance with the facts presented by the bud-development of Pe - 

 rophora viridis. 



