]38 



LECTURE Vn. 



homogeneous granular texture when broken up under the microscope. 

 In the Pennatula phosphorea the ova, of the size and form of poppy 

 seeds and of a yellow colour, are found at the back part of the pinnje. 

 In Virgularia mirahilis the small, round white ova are seen in spring, 

 ranged in a double transverse row under each of the lateral fleshy 

 expansions, forming external projections ; but as the embryo acquires 

 its ciliated superficies and yellow colour, it advances slowly into the 

 body of the polype beneath which it was developed, and begins to 

 manifest contractions of its tissue and revolving movements, by which 

 it escapes from the mouth of the polype and swims slowly away.* 

 This locomotive faculty is much abridged, if not wholly lost, when 

 the animal has acquired its mature form and begins to propagate by 

 continuous gemmation. The Pennatulffi do not swim, as has been 

 supposed, by the movements of the pinnaj, but move languidly ; most 

 of the family remain at the bottom ; and the Virgularice and Pavo- 

 narice have one end stuck deeply in the sand or mud, into which they 

 can retract themselves. In the Lohularia the ova are formed and 

 matured in the longitudinal mesogastric folds of the polypes, f Ellis | 

 has well represented them, in groups of from five to eight in each of 

 the canals below the polypes, and also the larvte in their passage 

 through the transparent bodies of the polypes. When the larvse have 

 acquired their ciliated surface and red colour they become detached 

 from the mesogastric folds, and work their way slowly through the 

 polypes when the bodies of these are expanded and distended with 

 water. Certain individuals, or groups of individuals, of the Lohularia 

 digitata have been found to develop only sperm-sacs and spermatozoa. § 

 The fleshy substance of the Acti7iice, LohularicB and Alcyo7iia is 

 strengthened by numerous minute calcareous spiculte. Analogous spi- 



cuIeb, but of varying and cha- 

 racteristic forms, strengthen 

 likewise the fleshy crust of 

 the red corals, jointed corals, 

 and Gorgoniae ; but to these 

 spiculjB is superadded the in- 

 ternal branched axis, which, 

 according to its composition 

 and structure, characterises 

 the diti^erent genera of this 

 group. The spiculte of the 

 cortical part consist princi- 

 Lobophyiia anguiosa. p.^lj^ ^f carbonatc of lime, like 



the denser skeletons of the MndreporidcE, Jig. 66, with which they 



66 



* CXVIII. p. 350. 

 X CXX. pi. XX. 



t CXIX. p. 104. 

 § CXV. p. 101. 



