ON THE BRITISH SPECIES OE ORISIA. 145 



but when formed, some of them give rise to fresh stems, which 

 are the startiug-points of new colonies. Or, again, some of the 

 specimens found in the summer have resulted from colonies 

 which developed ovicells in the earlier part of tlie year, and 

 which, after losing these structures, again burst out into 

 renewed growth ; in some cases leaving a single ovicell on the 

 colony as some indication of their past history. In the spring, 

 ovicells, when present at all, are found in large numbers, and 

 those well-developed colonies which do not possess them at 

 this period are probably in most cases of the male sex. Thus, 

 in order to find spermatozoa in April, it was generally quite 

 sufficient to select any colony in which there were no ovicells, 

 while spermatozoa were not discovered in any of the cases in 

 which ovicells were present. 



In the early spring the discoloured stumps of colonies which 

 grew during the preceding year are found ; from various parts 

 of these, new growing-points are developed, and give rise to the 

 colonies found at a slightly later period. The production of the 

 enormous number of embryos then developed seems to exhaust 

 the energy of the colony, whose growth practically ceases for a 

 time, many of the branches being thrown ofi". After a period 

 of rest, growth recommences with great vigour, and by the 

 middle of the summer large and highly branched colonies are 

 again found, although now, as a rule, with no ovicells. 



Number of Zocecia in the Internode, Mode of Branching, &c. 



Most of the previous accounts of Crisia merely mention the 

 limits between which the number of zooecia in the internode 

 may vary in the several species. Thus Hincks^ says of 

 C. eburnea, " 3 — 9 cells in an internode ;^^ while Johnston^ is 

 a little more explicit, stating that '' there are from two to 

 five, sometimes seven, and very rarely even nine, cells in each 

 internodial space " in the same species. It appears to me that 

 it is quite impossible to define accui'ately the several species 



' 'Britisli Marine Polyzoa,' p. 421. 

 - ' Britisli Zooplijtcs,' ed. 2, p. 284. 



