214 HYATT, 



ertheless more embryonic in some respects than the evag- 

 inatory region in the same genus, or in Plnmatella. 



Nothing can be more opposed to the fully evaginated 

 state of the adult Cristatella than the embryonic aspect 

 of the lophophore, and it will be readily perceived, from 

 the homology suggested between the original cell of the 

 colony, and the sack-like coenoecium, that the latter has a 

 more embryonic aspect than the branching coenoecium of 

 Plumatella. This is the only point in which the lopho- 

 phoric and coenoecial regions agree ; in all others they are 

 at variance. 



Such would be inferred to be their most appropriate 

 relationship, from the fact, that all the modifications of 

 the evaginatory tube were found to be due to the more 

 fundamental changes of the coenoecium ; whereas, those of 

 the lophophore were not dependent upon any of the 

 changes in the other two. Thus the lophophoric adds its 

 greatest increment of complication, the "fully developed" 

 arms, in the second genus of the sub-order, whereas the 

 coenoecial more gradually progresses and acquires its 

 greatest anatomical increment, the reticulated walls, only 

 in the last genus. Both are most complicated in Crista- 

 tella, but both arrive at the highest degree of complica- 

 tion by difterent methods. 



The evaginatory region does not agree with either of 

 these ; the increment of complication is gradually and 

 slowly added, and no new organs or sudden develop- 

 ments of particular parts take place. In all its relations 

 with the regions above and below, this region occupies 

 an intermediate place. 



In fact, the mutual influence of the modifications in 

 one region upon the organs of another is proportional to 

 their positions in the body of the adult, and the times of 

 the acquisition of the adult characters by such region 

 during the development of the individual. 



The modifications of the coenoecial region, situated as 

 it is at the anterior pole, bear directly on the next region, 

 the evaginatory, changing its organs greatly, but it does 

 not afiect the lophophoric at the posterior pole of the 

 body. The forces or organic momenta of the changes 



