16 BULLETIN OF THE 



22, 29, gn.) lies betwoen vas deferens and nephridium, is elongated trans- 

 versely, and slightly constricted in the median plane. One can distin- 

 guish a central region composed of fine fibres running transversely, and 

 a cortical region of cuboidal, deeply staining cells with large clear nuclei. 

 I have not succeeded in tracing any peripheral fibres from this gan- 

 glionic mass, as Ehlers has done in another Endoproct. 



III. Non-sexual Reproduction. 



1. Architecture of the Stock. 



Urnatella forms stocks by budding. As in other Bryozoa, the buds 

 are normally produced in a very regular manner. I believe that I have 

 determined the law in part, although it has exceptions, as the law 

 of b adding in every Bryozoan stock has. As Leidy has stated, several 

 vertical stalks may arise from the same horizontal plate. A single stalk 

 may remain unbranched, giving rise to new individuals at its distal end 

 only, or it may give rise to branches which come off irregularly from a 

 few segments. Usually only one branch arises from a single segment, 

 but occasionally two do so (Plate V. Figs. 35, 38). 



The length of these branches and the number of their segments decrease 

 towards the distal end of the main stalk, and the conclusion seems jus- 

 tified that it is only at the distal end that they are formed. Excepting 

 for these occasional branches, the lower segments of the stalk are bare of 

 any branches or polypides. The distal end, however, is usually crowded 

 with polypides so thickly as to make it difficult to count them or to de- 

 termine their points of attachment (of, Plate V. Fig. 30). 



A very casual observation, however, shows that the buds from the 

 main stalk are of two kinds; first, those which have given rise to a 

 linear series of segments at the distal end of which is a calyx, and these 

 are what I have called branches ; and, secondly, those consisting of a 

 stoIon-Yiko. process, from one surface of which arise calyces resting upon 

 a stalk of usually one segment only. The surface of the stolon upon 

 which such polypides are placed is a definite one, namely, that which is 

 turned towards the distal end of the main stalk. The budded branches 

 and also the stolons are grouped j^pon the oral side of the adult stalk. 



In the clearest cases, in young or not too richly branched stocks, I 

 find the branch arising on the oral surface of the segment, and between 

 two stolons, which are therefore more nearly lateral (Plate V. Figs. 37, 

 38, 40, 42). 



