364 E. R. CUMINGS POSITION OF THE MONTlCULirOKOlDS 



somewhat diagrammatically the manner of origin of the remarkable 

 Fenestella-like branches or rays. The first indication of these rays is 

 the tendency of certain zooecia to arrange themselves in parallel pairs 

 at rather regular intervals, between which the arrangement is still some- 

 what irregular. The interzooecial walls of these parallel juxtaposed 

 zooecia next become somewhat thickened, giving rise to the ill defined 

 vertical median lamina of the sinuous anastomosing branches of the 

 colony. A young colony in which the infundibular superstructure has 

 not begun to arise presents a curious resemblance to one of the star- 

 shaped maculae of a Constellaria. The remarkable features of this spe- 

 cies indicate very impressively how tenuous after all is the line between 

 the Trepostomata and the other orders of the Bryozoa. Ulrich (13, 14) 

 has pointed out at sufficient length the affinities of the species with the 

 Cryptostomata. Its affinities with the Trepostomata are conclusively 

 shown by its mode of development. 



Development of Bhombotrypa 



Figure 40 shows a transverse* section cutting somewhat above the pro- 

 toecium of a young colony of Rhomhotrijpa quadrata. The general ar- 

 rangement of the zooecia is the same as in the other genera studied. 

 The ancestrula gives rise to two buds. The primary buds and ancestrula 

 are set off from the posteriorly directed buds by a thickened wall, as in 

 all other genera. A noteworthy feature of this section is the presence 

 of acanthoporcs in the initial region. They are not present in the ma- 

 ture portion of colonies of this species. This may be taken to indicate 

 the affinities of this genus with Amplexopora. 



Development of other Genera 



Several sections have been obtained of Amplexopora scplom, showing 

 the initial region. Their appearance is the same in all essential respects 

 as tluit shown in figure 40 of Rlioiiiholrijpa. Acanthoporcs are present 

 in abundance, e\(Mi in the i)riinary buds. 



A few sections show the initial region ot* what appears to be a species 

 of Tlornotrypa. The arrangement and budding order are the same as in 

 Prasopora, and the thickened posterior walls of the ancestrula and pri- 

 mary buds are exceptionally well shown. 



Discussion and Conclusions 



The form and structure of the ])rimary zooecium of the colony of the 

 Trepostomata and the arrangement of the buds and their derivation 



