72 REPORT OX THE PENNATULIDA. 



cavities ; and then tlie extension of the mesenteries to the bottom of 

 the polype-cavities, and the thickening of their free edges to form the 

 mesenterial filaments, are all that is necessary to complete the develop- 

 ment of the polypes. 



We shall only notice one other point : the great retractor miuscles 

 of the polypes appear at a very early stage, when the stomach cavities 

 are mere pits and no traces of the tentacles have yet appeared. They 

 are shown at about this period in Fig. 6, ^j. By studying the early 

 stages carefully it can be seen that these muscles are portions of the 

 great subcutaneous system of muscles which origmally extended all 

 round the rachis, and which persists comparatively unaltered on the 

 dorsal and ventral surfaces (Fig. 6, hn), portions the direction of 

 which has become changed by the pittings in of the surface which 

 fox'm the stomacli-cavities of the polypes. 



From the mode of formation of the body-cavities of the polypes out 

 of parts of the canal system of the rachis, it is clear that the continuity 

 between these two systems which we have seen persists in the adult 

 is a primitive one, and not a secondary one acquired in the course of 

 development. 



5. — Anatomy of tJie Zooidg. — 



The zooids of Virguliria are simply arrested polypes, polypes which 

 have stopped short at the stage of development represented in Fig. 6. 

 They have no tentacles ; their stomach-cavities are merely blind 

 sacs, the walls of which are not thrown into folds ; and, in fact, they 

 resemble these rudimentary polypes in all points except in having no 

 reproductive organs developed in connection with them. 



6. — Zoological Position and Ajfi)iities. — 



The position of I'irgularia relatively to the other two genera is 

 shown in the table on page 1 of this report. The generic characters, 

 as stated by Kolliker,* are as follows : — • 



" Genus : ]'irgularia. Leaves small, attached to the rachis by 

 wide bases, ending below in a long series of undeveloped leaves. 

 Polype cells fused together along the greater part of their length, 

 either in a single row, or else alternating so as to give the appearance 

 of two rows. Tentacles cylindrical, with short pinnules. Reproductive 

 organs, as a rule, contained within the rachis at its lower end, and 

 only in a single species found in all the leaves. Zooids lateral, in 

 single or multiple rows between each pair of leaves. Eadial canals in 

 two longitudinal ridges along the ventral side of the rachis. A terminal 

 dilatation at the end of the stalk. Stems cylindrical. Calcareous 

 spicules absent in the rachis, but present in some cases in the stalk in 

 small numbers." 



Of the nine species of this genus distinguished by Kolliker the 

 descriptions of five are based on the examination of single specimens 

 only ; and of the remaining four there is no doubt whatever that the 



Kiilliker, " Alcyonarieu," p. 182-3. 



