THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XX. — Development of Fenestella ; by Edgar Roscoe 

 Cumings, Ph.D. (With Plates V, VI, and VII.)' 



Introduction. 



During the past two years, the writer's studies of the devel- 

 opment of Paleozoic Bryozoa* have brought out some very 

 interesting points bearing upon the earliest stages of Fenestella. 

 The present paper deals with the development (astogeny) and 

 morphology of Fenestella, and is based entirely upon calcified 

 material from the Hamilton formation of Thedford, Ontario. f 

 This material consists of numerous bases of Fenestella colonies. 

 In these, the minutest details of internal structure are pre- 

 served with remarkable fidelity. The method of study has 

 been the preparation of both thin and serial sections. The 

 latter were obtained by slowly grinding down the bases and 

 accurately drawing each stage as seen by reflected or in some 

 cases by transmitted light. The specimens studied are in vari- 

 ous stages of growth. Some represent the bases of adult 

 colonies from which the adult (ephebastic) portion has been 

 lost; others are minute bases, which in their growth never 

 proceeded farther than the nepiastic stage. In these nepiastic 



* In a former paper, a classification of the growth stages of the "bryozoan 

 colony was given, together with a general classification of the growth stages 

 of any colony belonging to any gronp of organisms. The terms applicable 

 to the growth stages of any colony are : Nepiastic, neanastic, ephebastic, and 

 gerontastic, corresponding to the well-known terms nepionic, neanic, ephebic, 

 and gerontic y applicable to the growth stages of the individual. Dr. Kuede- 

 mann has recently proposed the term astogenetic with reference to the colony, 

 as the term parallel with ontogenetic with reference to the individual. The 

 astogenetic stage of a colony, therefore, corresponds with the ontogenetic 

 stage of an individual. 



f This 'Fenestella is probably the form listed by Grabau as Semicoscinium 

 labiatum. 



Am. Jour. Sci. — Fourth Series, Yol. XX. No. 117.— September, 1905. 

 12 



