ofy^. ^rella latitenta, Pote. 301 



in some species of Spongilla and not in others must be accepted 

 as analogous to the presence of the cirri on the statobList of 

 PectinateUn magnifica^ and their absence on that of Plumafelhi, 

 or, to adduce a more homely exanijile, the presence of horns 

 in most cattle and their absence in the " Galloway breed." 



Tlius the " tubular prolongation of, and not addition to, 

 the chitinous coat of the statoblast in Carterella latitenta, as 1 

 must now view it, is so much longer than that of C. teno- 

 sperma^ that it bears the proportion of 5 to 1, or l-90th inch 

 in the former to l-450th inch long in the latter (compare 

 fig. 2,/, in PL XIV., with %. 1, ./; in pi. xvii. ' Annals,' 

 /. c.) ; while in other respects it is much the same, beitig 

 in direct continuation with the chitinous coat and open 

 or closed at the free end, as the case may be. On the 

 other hand, the '' cirrous appendage" may be single or 

 double (PL XIV. figs. 2,^7, and 3, gg)^ and commencing 

 in a broad ribbon-like form about l-180th inch wide, 

 which embraces the tubular prolongation after tlie manner of 

 a flange, about 1 -360th inch from its free end (fig. 2, g m)^ 

 goes on diminishing in width for a certain distance, when tlie 

 ribbon-like portion (fig. 2, to ra m) may cease, and the cutus 

 may end in a single or double, round or cord-like filament, 

 afterwards continuing a whip-like diminution to its termination, 

 also like that of CartereUa tenosperma (fig. 2, i I, and fig. 2, 

 pi. xvii. ' Annals,' I. c), altogether about one third of an 

 inch long, or twelve times the diameter of the statoblast ; but 

 this, of course, is subject to much variety, as no two stato- 

 blasts are exactly alike in their measurements. The com- 

 mencement of the cirrous appendage in C. latitenta^ which, 

 although broad, is very thin and transparent, may, if carefully 

 examined under a microscope, be found to have a thickened, 

 round, cord-like margin on one or both sides (fig. 2jkk), 

 which, wlien traced to the termination of the ribbon-like por- 

 tion, leave it separatedly in the round shape mentioned ; 

 generally one side is thicker tlian the other, while the latter 

 often becomes so diminished as to disappear altogether, and 

 thus leave the intervening membranous expansion in the form 

 of a simple alar appendage. This, which renders the cirrus 

 so much like a ribbon in C. latitenfa, is not altogether absent 

 in C. tenosperma^ where it may frequently be seen to unite 

 the filaments into a disk-like form around the tubular prolon- 

 gation, especially in C. tuhisperma (figs. 7, 8, and 9), when, 

 as before stated, it recalls to mind the webbed arrangement of 

 the tentacles round the mouth or beak of a Cephalo])od. Tims, 

 although difixirently formed in difierent species, the plan of 

 development in the cirrus is the same ; and thus the greater 



27* 



