128 REPORT ON THE PENNATULIDA. 



upwards, and on reaching a point Jin. from the top of the rachis 

 bends back on itself for a length of about iin., ending in an extremely 

 slender and flexible thread. 



In the second specimen, which has a total length of 5iin., of which 

 the stalk forms the lower 2in., and which has thirty-one leaves on each 

 side of the rachis. each of the larger ones coasistmg of twelve polypes, 

 the general relations are very similar. The stem is again distinctly 

 quadrangular at the junction of stalk and rachis, its sides being even 

 more decidedly concave than m the former specimen. The quad- 

 rangular character is preserved until very near the bottom of the 

 stalk. As before, the stem diminishes in diameter very slowly at first, 

 but rapidly in the last half inch. It extends to the bottom of the 

 stalk, and then turns back on itself for a length of Jjin., forming a hook 

 and ending in a very slender thread. 



In the rachis the stem becomes cylindrical almost at once, and, 

 unlike the former specimen, slightly increases at first in size, its 

 greatest diameter, 0-04:7in., being attained about ^in. above the com- 

 mencement of the rachis. From this point it tapers gradually to its 

 upper end. It extends up as far as the level of the eighth pair of 

 leaves, gin. from the top, and then bends back on itself, forming a 

 loop about ^in. long, and ending as before in an exceedingly slender 

 thread. 



In the Oban specimens we have been able to confirm the above 

 description to a certain extent. Owing to the thinness of the wall of 

 the lower end of the stalk, it is easy to satisfy oneself that the stem 

 extends quite down to the bottom and then turns back on itself for a 

 certain distance ; also, that it is thin and flexible at this lower end. 

 In the rachis it is, as shown in Fig. 3 c, oval in transverse section ; 

 and concerning its extent upwards, it appears, so far as can be deter- 

 mined by external manipulation, to stop about half an inch from the 

 top. 



The stem consists of a dense fibrous matrix, in which the fibres 

 are mainly concentric, but partly radial, impregnated with calcareous 

 salts. Unlike Fnniculiiia, the central part of the stem is as firmly 

 calcified as the exterior. 



The quadrangular character of the stem in the stalk is of interest, 

 as it has hitherto been very generally considered diagnostic of 

 Funioilina, which, however, unlike Pcnmitula, preserves the quad- 

 rangular form in the rachis as well. 



Concerning the proportions of the stem at different parts of its 

 length, the remarks that we have already made when considering 

 Fanlculiiia* apply also to PeiDUitula, the proportions being precisely 

 those which, mechanically considered, adapt it most perfectly to the 

 erect ^posture with the stalk planted in the mud of the sea bottom. 

 We shall return to this point further on. 



( To be continued.) 



* S'tpra, ?pp. 5-6, 



