82 THE VOYAGE OF H.M.S. CHALLENGER. 



long and narrow and form, when closed, a cone over the mouth of the polyp, or they are 

 short and flap-like so that the closed mouth of the polyp appears evenly truncated. 



The calyx scales have generally the form of an irregular quadrangle. The nucleus, 

 consisting of small calcareous granules, is always excentric, whereby the quadrangle in 

 all cases appears inequilateral. From the nucleus little protuberances radiate outwards 

 towards the edges. The free edge of the scale is smooth, the covered edge is provided 

 with small teeth and projectiug spines. The scales of the ccenenchyma, which are so 

 placed as to cover each other with their edges, are very irregular, oval, or angular 

 little discs, always much smaller than the scales of the calyx. One can distinguish an 

 outer layer of flat, warty, little discs, and a inner layer of spiny spicules which are more 

 spindle-shaped, sometimes branched, and recaU the spicules of the Miiriceidae. 



The bilateral symmetry is evident in the internal organization of the polyp as weU 

 as in the form of the calyx. The oesophageal tube is laterally compressed, the two 

 ventral and the dorsal mesenterial folds are shorter than the lateral ones and inclose a 

 ventral and a dorsal chamber, which are distinctly smaller than the six lateral ones. 

 During life the polyps may be stretched out straight from the stem and may again be 

 bent in towards the stem, in this position they are found in all dead and dried specimens 

 or in those preserved in spirits. The canal system of the colony consists of eight 

 longitudinal canals, which are arranged strictly radially around the axis of the stem 

 and are separated from one another only by thin septa. Into these canals, which 

 traverse the entire stem, a net-like anastomosing system of narrow canals opens, which 

 originates from the digestive cavities of the- polyps, A canal always arises from each 

 mesenterial chamber of each polyp, and unites in a net-like manner with its fellows in 

 the ccenenchyma. Ova and spermatozoa arise on the mesenterial folds below the 

 oesophageal tube ; hermaphroditism appears not to take place ; on the contrary, in 

 Prlmnoa fiagellum at least, the colonies are dioecious. New polyps arise by budding 

 from the canal system in the internodes between two whorls of polyps, at first they are 

 situated ventrally to the base of a whorl of polyps and as they grow larger they gradually 

 become further removed from it by simultaneous growth of the internodes. The growth 

 of the colony accordingly takes place in the internodes of the whole stem at the same 

 time. A resolution of the polyps appears to set in gradually at the base of the stem. 

 The lowest circles have generally a smaller number of polyps than those higher up. 

 The most vigorous development always takes place in the middle of the stem. The 

 number and arrangement of the cal5''x scales is precisely the same in the youngest buds 

 as in the most developed, so that the scales increase in size with the growth of the 

 calyx. 



The species of this genus are inhabitants of deep water, and as yet have only been 

 found in seas south of the, equator, in water of low temperature, and at depths of 40 to 

 600 fathoms. 



