HYDROZOA. GRAPTOLITOIDEA 



57 



beyond the distal 1 end of the common canal. At the 

 proximal end of the polypary there is a small conical body, 

 termed the sicula (fig. 13, c, s), which will be described 

 more fully below (p. 61). 



The soft parts of the graptolites are of course unknown, 

 but from comparison with living hydroids which have a 

 similar skeleton, we may consider it probable that each 

 hydrotheca lodged an individual polyp, and that these 

 were connected by means of the ccenosarc which occupied 

 the common canal. 



a 



<z 



-tn 





*><= 



IYb 



- — k 



i a. 





■S 



Fig. 



13. a, Portion of Monograptus personatus ; b, diagrammatic vertical 

 section of the same ; c, Monograptus colonus, Coniston Grits, with 

 sicula (s) ; d, Diplograptus foliaceus, LlandeiloBeds, with virgula (a), 

 and the position of the embedded sicula (s) indicated. All enlarged. 

 a, position of virgula in wall of b ; c, common canal ; h, hydrotheca ; 

 m, mouth of hydrotheca; s, sicula. 



In the form just described {Monograptus) the polypary 

 is always simple, but in many genera it consists of two 

 or more branches or stipes. When there are several 



1 The proximal end is that which in recent hydroids is attached ; the 

 distal is the free end. In the graptolites the proximal end is formed 

 first, the distal end last. The side of the graptolite on which the hydro- 

 thecaa occur is spoken of as the ventral, and the opposite side as the 

 dorsal. 



