THE GRAPTOLITES AND CORALS 283 



of budding (Fig. 84). These are arranged along two 

 branches, or stipes, hanging down almost vertically but 

 slightly divergent. Each stipe consists of a series of 

 somewhat cylindrical cups, or thecce (hydrothecse), which 

 lodged a polyp each, and a common canal uniting their 

 inner ends. The sicula and stipes constitute thepolypary,oic 

 complete skeleton, of the colony of polyps. The end at 



FlG. 84. DlDYMOGRAPTUS MINUTUS, ToRNQUIST, LOWER 



ORDOVICIAN (ORTHOCERAS LIMESTONE), OLAND. 



Initial portion, reverse side (Xig). (After Holm.) S', Apical part of 

 sicula; S", aperture of sicula; Cr. C., crossing canal; c,c. t common 

 canal ; i 1 , 2 1 , first and second thecae of first stipe ; i 2 , first sicula of 

 second stipe. 



which is the sicula is called the proximal end, the opposite 

 end the distal. 



The two stipes are not, however, absolutely sym- 

 metrical. The first theca of one stipe arises directly from 

 the sicula, and successive thecae, with the common canal 

 pertaining thereto, are budded off in turn ; but the first 

 theca of the other stipe is budded off from the first theca 

 of the first stipe, so that its portion of common canal has 



