350 CUMINGS AND GALLOWAY MORPHOLOGY OP TREPOSTOMATA 



alone, the problem was finally successfully attacked from the standpoint 

 of colonial development (astogeny). The senior author's paper on the 

 development of the Trepostomata (8)', published in 1913, leaves no 

 doubt of the Bryozoaii affinities of the order. 



The results presented now are only a part of the mass of exact data 

 that has accumulated during these years. All of it is confirmatory of the 

 relationsliips ijidicated by development, and has led us to express a de- 

 gree of confidence in our interpretations of certain peculiar structures 

 that, in the absence of such conclusive evidence, we could not have had. 



Nearly all of our knowledge of the morphology of the Trepostomata 

 has been gained through the work of Nicholson (22-25), Ulrich (28-3J:), 

 ITlrich and Bassler (35), Bassler (1^), and the writers (6-10). In 

 this list the name of Ulrich stands preeminent. Had the internal struc- 

 ture of recent Bryozoa been studied with equal thoroughness our problem 

 of the interpretation of trepostome structure would have been very greatly 

 lightened. As it is, we are still left in the dark in regard to a number of 

 points. We have, to be sure, the works of Milne-Edwards, Busk, Waters, 

 Nitsche, Hincks, Smitt, and Harmer, and especially of Calvet and Lev- 

 insen. Nevertheless, one still looks in vain for an elucidation of colony- 

 building in the recent Bryozoa, such as the absence of soft parts has made 

 necessary in Paleozoic forms. 



For example, the exact manner in which the interzooecial wall must 

 have been built up in the Trepostomata is beautifully revealed in the 

 illustrations accompanying the present paper ; but of the manner in which 

 the interzooecial wall is actually built in recent Bryozoa most closely re- 

 lated to the Trepostomata, namely, in Heteropora and in the Cyclosto- 

 mata, we know little. It will be necessary to study the recent Bryozoa ■ 

 by the meth(tds now employed with such success in the study of the 

 Paleozoic Bryozoa. Until this is done some points at least must remain 

 obscure. 



Cysts and Cystiphragms 



in general 



One of the most striking, and indeed one of the most extraordinary, 

 features of the Trepostomata is the structures known as cysti]:)hragms. 

 Cystiphragms occur rt^gularly in several genera and sporadically in many 

 others. In MonticuUpora, Tlomotrypa, Peronopora, Tlomotrypella, etcet- 

 era, these structures are invariably present and preeminently character- 

 istic. In Amplexopora, Baiostoma, Heterotrypa, TIallopora, etcetera, 

 they are usually absent. In fact, structures exactly like cystiphragms in 



- Figures in ( ) refei- to bibliography on page 366. 



