50 BULLETIN OF THE 



more evident in the adult, and when new individuals arise distad to any 

 two, one of the new ones is median (ancestral branch), the other lateral. 

 (So terminal individual of rows 11 and 10 ; 22, 23 ; 43, 44 ; etc.) In 

 the diagram, however, I have not always indicated which is the median 

 and which the lateral branch, for in the older parts of the colony, owing 

 to a shoving of individuals, it is not easy to distinguish them. 



Lateral branches appear usually to be given otf towards the axis. 

 Here, as in Bugula, the lateral branches tend to be longer ; the ances-, 

 tral, shorter. 



It is evident from the diagram that latei'al budding is most frequent 

 at the margins of the corm, i. e. that part lying posterio-dextral or poste- 

 rio-sinistral of the primary individual, and that the descendants of the 

 two lateral individuals of the four belonging to generation II. are more 

 numerous than those derived from the middle two. Finally, it is evi- 

 dent that the number of individuals per unit of arc will be the same for 

 arcs of all radii, and therefore the rate of increase of individuals will 

 diminish through successive generations. 



In Crista ehurnea, Linn.,^ we find the same laws illustrated. The 

 architecture of the genus has been carefully treated of by Smitt ('65', pp. 

 115-142) as forming the basis of classification. Barrois ('77, pp. 76-85) 

 has described in a masterly way the formation of the young stock of 

 tubuliporid Cyclostomata, and the relationsliips of the different types 

 of budding in this group. Harmer ('91, pp. 145-173) has recently dis- 

 cussed the architecture of the stock in British species, adopting Smitt's 

 graphic method of showing it. I have found his paper of great value 

 for my purpose. 



This species grows as a shrub-like stock upon floating eel-grass, etc. 

 I was wrong in saying, in my Preliminary ('91, p. 282), that Crisia has 

 its branches united in pairs. The comparison of this species made by 

 Barrois ('77, p. 82) with the "geniculata form" is conclusive evidence, 

 to my mind, that the apparent double row is in reality a single one, and 

 that such a branch as 18, Figure 65, is to be represented by a single 

 line in the diagram Figure 65*. We find here terminal and lateral 

 branches ; no true dichotomy. Branches are given off on the side awai/ 

 from the axils, as in Lepralia, not as in Bugula. (But branch 11 is an 

 exception to the rule.) They are given off, as Harmer ('91, p. 131) 

 has shown, alternately to the right and left. 



^ This is the only species of Crisia given by Verrill, and, since my species 

 is very common, it must be the one to whicli he refers. Moreover, it agrees 

 fairly well with Harmer's diagnosis ('91, p. 131). 



