90 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



permanent condition in the ancestor being only the transient 

 condition in the descendant. Two distinct lines seem to be 

 traceable, from two types of Flagellates ; one producing the 

 small class of Heterokontae, the other the remaining green 

 algae. Some authors have further divided the latter, and as 

 the Heterokontae derive their name from the unequal cilia of 

 the motile stage, the name Isokontae has been proposed for 

 algae whose motile spores have two equal cilia ; the Akontae 

 for those with no motile ciliate stage, and the Stephanokontae 

 for those with many cilia arranged in a circle. But this desire 

 for symmetry seems to come under the head of " trop de zele " ; 

 there is fully as much reason to suppose that the Conjugales 

 (Akontae) have lost the motile stage possessed by their ances- 

 tors, and that some at least of the multiciliate organisms are 

 modifications of the biciliate type. See Davis, 1908. 



From the nature of the case, all the forms here to be described 

 must be arranged in a linear series, but it is to be hoped that 

 no one will suppose that their relative rank can be determined 

 by their position in the series. The general arrangement is 

 from the more simple to the more complex ; Order A, the 

 simpler, being followed by Order B, the more complex ; and in 

 each order family a, the simpler, is followed by family b, the 

 more complex; but it is almost always the case that family z, 

 the most complex of Order A, is considerably in advance of 

 family a in Order B. A glance at one of the diagrams that 

 have been made to show the probable filiation of the different 

 types will give an idea of the complexity of the matter. Change 

 is not necessarily progress ; retrogression is often evident. The 

 preservation of the individual or of the type may be secured by 

 very many appliances or adaptations, thus forming diverging 

 lines of development, some reaching a point where further 

 progress in that line is impossible, others continuing, perhaps 

 giving off lateral lines here and there. All schemes of showing 

 these tendencies and results assume the former existence of in- 

 termediate forms, now extinct; and so imperfect is our knqwl- 

 knowledge of what remains, that it is evident that many schemes 

 may yet be proposed before we have one satisfying all the 

 requirements. No attempt will here be made to give any such 



