24 W. G. KIDEWOOD. 



a " lip " to the margin of each tube — and as apical growth continues and they 

 themselves come to occupy positions successively more remote from the apex, they 

 make their tubes longer and longer by additions to the margin, and they fill in the 

 spaces between the tubes with softer common test, so that the part of the branch in 

 which they occur l)ecomes thicker and thicker. Since, apparently, this makes the 

 tubes uncomfortably long, a shortening of them is effected by the successive 

 formation of concave septa at the basal ends at such a rate as to leave the inhabited 

 part of each tube about 8 or 12 mm. in length.* 



Polypides. 



The polypides are deeply pigmented and show conspicuously through the test. 

 Most of them are in a state of contraction, and their plumed ends are situated 

 about 5 mm. from the openings of the tubes in which they dwell ; a few, however, 

 are moderately expanded, and the plumes of these project slightly beyond the 

 openings of the tubes. Not more than one fully-grown polypide is found in each 

 tube, but from two to nine l)uds of various sizes are connected by their stalks with 

 the end of the stolon of the individual to which the tube may be said to belong. 

 The buds are usually crowded at that extremity of the polypide which is farthest 

 from the opening of the tube, Lying freely in the tube in the vicinity of the 

 buds an ovum sometimes occurs, rarely two or three ; the ovum is oval and 

 yellowish-white, and measures • 5 by • 6 mm. or * 6 by • 7 mm. The ova are seen 

 in figs. 3 and 4 as small whitish oval patches. 



The polypide is about three times as long as that of Cephalodiscus dode- 

 calophufi. The length of the body from the front of the buccal shield to the end 

 of the visceral mass is 4*5 mm., whereas in C. dodecalophus the corresponding 

 measurement is 1 • 5 mm. Tlie body is about 1 mm. wide, and fits fairly closely 

 in the tube, the interior of which is not more than 1 " 2 or 1 • 3 mm. across. 



When removed from its tulje, a polypide and its buds present the appearance 

 shown in fig. 7, plate 3. The l)uds are contracted and have their stalks twisted about 

 one another in a manner which is obviously unnatural and is doubtless caused by 

 the irritation set up liy the fluid in which they were killed. AYith a little care the 

 stalks of the buds of the formalin-preserved material can be unravelled (fig. 8) ; 

 the material fixed in Perenyi's fluid and that fixed in picric acid solution is, 

 however, too brittle to allow of any disentangling of the stalks. 



* The above was written before the publication of Harmer's report on the Pterobranchia of the ' Siboga ' 

 Expedition, and it is interesting to note that in one of the new species described by him (C. levinscni) the 

 polj-pides are similarly isolated, each tube of the tubarium being occupied by one pol;\'pide and its buds, and 

 that the explanation of the growth of the colony which he puts forward (10, p. 11), includes as its essential 

 feature the migration of the buds from the parental tubes, their crawlmg over the surface of the colony, and 

 then- subsequently establishing themselves in a suitable situation upon the surface, where they secrete tubes of 

 their own. (Later note, dated Sept. 15, 1906 : — The manuscript of the descriptions of C. nigresccns and C. 

 hoilgsoni (pp. 20-62 of this Report) was completed in August 1905 ; the first nineteen pages of the Report were 

 written in the summer of 1906). 



