6 REPORT ON THE PENNATULIDA. 



increasing flexibility in the upper. So marked, indeed, is this 

 adaptation of the shape of the stem to the form of the whole Pen 

 that it would alone be an argument of no inconsiderable weight in 

 favour of the erect position being the natural one. 



The lower part of the stem is very stiff, rigid, and brittle ; the 

 upper part is highly flexible, so that the two ends of the stem may be 

 brought together without the slightest danger of breaking. 



The stem itself, when freed from the ooenenchym, preserves the 

 very graceful curve already referred to, and well shown in Fig. 2., 

 which is drawn frona the largest of the three j)erfect specimens of 

 stems dredged up. 



Of the sixteen fragments of stems obtained, one 12 ins. in length 

 and with scarcely any curvature, must, from its size, have belonged to 

 a specimen at least as large as, and. probably larger than, the big 

 living specimen. The other fragments belonged, so far as we can judge, 

 to specimens averaging from 18 ins. to 36 ins. in length. In the curva- 

 ture and relative proportions of its parts the stem of FiDiiculina ofievs a 

 marked contrast to that of Virgularia, which we shall describe in a 

 subsequent paper. The differences are important, as they appear to 

 be directly connected with certain very marked differences in the 

 habits of the two genera. 



Transverse sections through the stem show that it consists of a 

 central core which is chitiuous and only very imperfectly calcified, and 

 an outer very hard, and firmly calcified rind, with a smooth outer 

 surface, and made iip of parallel lamellas. As the stem grows in 

 thickness by the addition of successive lamellae on its exterior, and as 

 the proportions between the hard outer rind and the soft core are much 

 the same in both young and old specimens, it is clear that the process 

 of deposition of calcareous lamellte on the outside must be accom- 

 panied by absorption of the calcareous matter previously deposited in 

 the more central portion. 



3. — The Polypes and Zooids — 



As among Pennatulida generally* the individual animals com- 

 posing the colony are of two kinds, distinguished as polijpes and zouids : 

 the polypes (Figs. 3 and 4, d) being distinguished by their greater size, 

 and by possessing tentacles and reproductive organs, while the zooids, 

 (Figs. 3 and i e), are smaller, and have neither tentacles nor i-eproductive 

 organs. 



In FunicuUna, the zooids form an irregular row on the mid-dorsal 

 surface (Figs. 3 and 4), on either side of iwhich the polypes are placed; 

 but the distinction between polypes and zooids is far less marked than 

 in the majority of Pennatulida, and it is very doubtful whether any 

 sharp line can be drawn between the two forms. In young specimens 

 especially the transition is a perfectly gradual one, and a complete 

 series of intermediate forms can be obtained between the largest 

 polypes and the smallest zooids. 



* Kolliker, op. cit., p. G. 



