SYSTEMATIC ACCOUNT 237 



He says that in C. detisus the tubes are straight and that in C. rarus they are irregularly 

 curved. While in C. densiis the tubes are 6 to 7 cm. long and the coenoecial substance 

 at the base free from sand particles, the tubes of C. rarus are only 4 to 5 cm. long and are 

 distinguished by the presence of sand grains in the coenoecial substance. But Ridewood 

 (1918 a, p. 40) has shown that these distinctions are the result of variations which do not 

 affect either the structure of the colony or the characters of the zooid. The colony when 

 first formed consists only of a few tubes, which, being unimpeded by anything in the 

 immediate vicinity, are irregular and even straggling. As the zooids multiply, the tubes 

 become more and more closely set and older tubes become longer and straighter, con- 

 sequently after a study of complete series of gradations between C. rarus and C. densiis, 

 he concluded that C. rarus is synonymous with C. densus. Even the differences in thickness 

 of the epidermis of the axis of the arms are such as might occur within the same species. 



Nothing more need be said to emphasize Ridewood's conclusions. The two specimens 

 obtained from station 190 both possess tubes which are mostly curved. The older tubes 

 are 5 to 6 cm. long and their distal parts straight. In one colony there are a few stray 

 sand grains embedded in the coenoecial substance, but in the other the sand grains and 

 diatoms are numerous. 



It may be added that the occurrence of sand grains in the common coenoecial sub- 

 stance is not constant, resulting from selection by the zooids, but depends rather on the 

 immediate surroundings. If the colony grows in unsheltered spots or at the base of 

 submarine rocks the particles which constantly rain from the upper regions of the sea 

 or drop occasionally from the sides of the rocks may fall on the colony and become 

 embedded in the common coenoecial substance. The quantity of sand grains on the 

 colony will depend on the intensity of the rain of particles from above, so that it is 

 possible to find colonies free from sand grains, or with only a few stray particles, growing 

 in the sheltered places. This is supported by the different colonies of the present 

 collection in which the quantity of sand grains, included in the common coenoecial 

 substance, varies markedly. 



Each tube is occupied by one zooid and its buds. In the preserved condition the 

 upper tip of the zooid is situated about 7 to 9 mm. below the ostium. The zooids are 

 pale white, but the arms are brownish. The body is straight, longer than that of other 

 species and measures 4 to 10 mm. from base of body to tip of arms. When a zooid is 

 viewed under a lens, two white elliptical patches can be seen slightly bulging out on 

 each side of the pharynx. They arise from the base of the collar region between the 

 opening of the rectum and the pharynx. These are the gonads, which are conspicuous 

 in this species. All the zooids which have been examined in section are hermaphrodite, 

 but both Ridewood and Andersson have observed male and female zooids, with paired 

 testes or ovaries. Ova occupy the upper part of the ovary, the lower part being filled 

 with yolk granules. Sometimes a few eggs are found in the basal part of the tubes. The 

 testis is a thick- walled elliptical tubular organ. The sperm are formed in the thick wall 

 and liberated into the central space from which they pass out through the short vas 

 deferens which opens between the rectum and the pharynx. 



