140 SIDNEY F. HARMER. 



there cau be no doubt that these structures disappear after the 

 end of the breeding season. I have looked in vain for any signs 

 of the absorption of the ovicells in Crisia; and the following 

 facts probably imply that they are simply thrown off from the 

 colony after the liberation of the embryos which have been pro- 

 duced in them. 



The typical spring form of C. eburnea possesses a con- 

 spicuous main stem, which forms an obvious central axis, from 

 which the rest of the colony comes off as a series of branches, 

 developed in regular alternation on opposite sides, and decreas- 

 ing in size fairly regularly from the base to the summit of the 

 colony. The main stem consists of perhaps eleven or twelve 

 internodes, each of which normally gives rise to a branch ; 

 and the branches themselves are usually provided with a 

 profusion of ovicells, many of which are still in process of 

 development, and most of which are near the ends of the 

 branches. 



In a colony of the same species found in May most of the 

 ovicells were at some distance from the ends of the branches, 

 owing to the development of several (7 — 8) zooecia above the 

 ovicells ; and the branches which bore ovicells had, in most 

 cases, completely finished their growth : very few ovicells, and 

 these of a weakly appearance, were being developed. Most of 

 the branches ended in slender internodes, in which growth was 

 no longer taking place, as was shown by the fact that no grow- 

 ing-points were left. The exhaustion of the colony was further 

 shown by the fact that some of the terminal internodes con- 

 sisted of no more than two or three zooecia, with no growing- 

 points. 



In the summer (August) large and highly branched colonies 

 with active growing-points are found, but they arc nor- 

 mally without any trace of ovicells. In many of these cases 

 it may be noticed that the main stem has been broken, and is 

 merely represented by its basal portion. The rest of the colony 

 will, in this case, probably consist of a small number of large 

 branches given off from the remains of tlic stem or of its 

 lateral branches, and in many cases the sharp contrast between 



