50 SYNOPTIC COLLECTION. 



absence of positive knowledge we can only reason from 

 analogy in regard to the rightful position of the genus in 

 a natural classification. In more specialized animals 

 such as certain corals, Polyzoa, and others, the free- 

 swimming colonies are derived from fixed colonial forms 

 which have lost their organs of attachment. It is, there- 

 fore, probable that when the life history of Desmarella is 

 known it will be found that the earliest stages of the 

 genus bear structural evidences of its descent from a 

 stationary form. If such evidences are not obtained by 

 accurate microscopical research, it might still be possible 

 that they have become wholly obliterated through the 

 action of the law of acceleration in development. The 

 colony of Desmarella is never large, numbering only 

 from two to eight zoons. 



In the light of the Flagellata already described, the 

 development of Proterospongia haeckeli S. K. is extremely 

 interesting. The animal begins its existence as a single 

 attached uniflagellate organism without a collar (PL 51, 

 fig. 19). Afterward the collar develops, and in this stage 

 the Proterospongia resembles a Monosiga. Next a muci- 

 laginous film is extended around the body below the col- 

 lar (fig. 20). By binary fission two zoons are produced 

 (fig. 21). Figs. 22 and 23 represent small colonies and 

 fig. 24 a large one of between forty and fifty zoons. 

 Cells migrate from the surface to the interior and become 

 reproductive in function. Some of the zoons in figs. 23 

 and 24 have drawn in their flagella and the body has 

 assumed an amoeboid appearance. This is in prepara- 

 tion for the encysted state (see fig. 24), after which the 

 mass breaks up into a large number of flagellate young. 



All the Mastigophora or Flagellata so far described 

 belong to the subclass Flagellidia. The following Dino- 

 flagellidia .are represented by Peridinium and the Cysto- 

 flagellidia by Noctiluca. 



The species Peridinium tripos Ehr. (PL 52, fig. i) is 

 provided with a transverse groove. According to the 



