174 F. B. Cumings — Development of Fenestella. 



the kathembryo. In Fenestella it is very large and in every 

 way similar to the protoecium (basal disc) of the Cyelostomata. 

 The ancestrula is the tubular superstructure of the primary 

 individual. It is a simple, undifferentiated, tubular zocecium. 

 The earlier formed zooecia (nepiastic zooecia) of the Fenestella 

 colony differ markedly in shape and size from later formed 

 (neanastic and ephebastic) zooecia. In every feature in which 

 they depart from the ephebastic zooecia of Fenestella they 

 approach the ephebastic zooecia of the Cyelostomata. 



From these observations, it may be reasonably concluded that 

 Fenestella as well as the entire order of Cryptostomata is 

 derived from the Cyelostomata. Certain other general conclu- 

 sions, more or less speculative, are suggested by a consideration 

 of the probable significance of the protoecium and ancestrula. 



The meaning of the degenerative metamorphosis of Bryozoa 

 has always been a puzzle to students of this class. The striking 

 analogy of this metamorphosis to the degeneration of an ordi- 

 nary polypide and production of a brown body, together with 

 the nearly identical life history of the regenerating polypide or 

 of ordinary buds and the primitive polypide issuing from the 

 kathembryo, have more than once led to the suggestion that 

 the primitive polypide is in the true sense a bud. The writer 

 is inclined to hold this view. Assuming, therefore, that the 

 primitive polypide is a bud, the following suggestions may be 

 made in regard to the significance of the metamorphosis and 

 of the resulting protoecium : 



1. In the primitive bryozoan, there was no histolysis of the 

 larval organs. The development was direct and resulted in a 

 primitive zooecium and polypide. 



2. This primitive zooecium was hemispherical in shape and 

 possessed a simple aperture in the center of its upper surface. 

 Some ancient types of Cyelostomata retain nearly such a form 

 of zooecium {Stomatopora of the Trenton, especially S. turgida). 



3. This primitive zooecium might now give rise to a linear 

 ad n ate series of zooecia, as in Stomatopora, or to a series of 

 superposed zooecia, as in the Trepostomata. By variations of 

 zoarial habit based upon one or the other of these fundamental 

 plans of budding all existing types of Bryozoa could have been 

 produced. 



4. In accordance with the law of tachygenesis, later in 

 the history of the bryozoan group a tendency toward concen- 

 tration of the early stages in development would arise. In any 

 colony the tendency to degenerate may be supposed to have 

 applied to the primitive polypide as well as to later ones, 

 and finally to have become an invariable part of its life history. 

 By the continued operation of the law of tachygenesis, the life 

 history of the first polypide became so abbreviated as to be 



