. Discovery reports. Discovery (Ship); Scientific expeditions. SYSTEMATIC ACCOUNT 229 cause these differences. Between these distinct forms there are colonies which are difficult to assign to either type. The existence of such intermediate forms proves that the external differences are the result of the amount of coenoecial material secreted by the animal. The coenoecium and spines are formed by the secretion of the coenoecial substance, laid down in thin lamellae. Increase in size is brought about by the deposition of lamellae over existing layers. Owing to differences in nutrition, and other
. Discovery reports. Discovery (Ship); Scientific expeditions. SYSTEMATIC ACCOUNT 229 cause these differences. Between these distinct forms there are colonies which are difficult to assign to either type. The existence of such intermediate forms proves that the external differences are the result of the amount of coenoecial material secreted by the animal. The coenoecium and spines are formed by the secretion of the coenoecial substance, laid down in thin lamellae. Increase in size is brought about by the deposition of lamellae over existing layers. Owing to differences in nutrition, and other causes, the amount of coenoecial substance secreted varies and this may account for differences which are observed between colonies dredged from different places. In the absence of zooids in the colonies obtained from stations 167 and 187, the structure of the coenoecium is the only evidence that these colonies are modified forms of C. hodgsoni. The colour of the coenoecium, the thickness and length of spines and the disposition of short branches are sufficient differences to separate them from Forms A and B (see below). Owing to subtle variations in the coenoecium of C. hodgsoni any attempt to give a comprehensive account of the structure may prove to be unsatisfac- tory. Generalization is rendered difficult by intermediate forms between the ex- treme types; but since the differences are only due to the amount of coenoecial substance secreted by the colony they do not affect the diagnostic character of the coenoecium as a whole. The colony is formed of a main stem which has many lateral branches. The stem and branches are hollow and the pig. i. C. hodgsoni showing the disposition in form A of continuous cavity opens externally by ostia and spines on a short hiteral branch. o,ostium;c, cavity numerous ostia. The sides of the lateral °^ coenoecium. branches and the edges of the ostia bear varying number of spines. These characters are constant in all the forms, and variations
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectscientificexpedition
