ALCVONARIA — PENNATULACEA 



359 



the autozooids and the siphonozooids. The former have the 

 ordinary characters of an Alcyonariau zooid, and produce sexual 

 cells ; the latter have no tentacles, a reduced mesenteric system, 

 and a stomodaeum provided with a very wide siphonoglyph. 



The arrangement of the autozooids and siphonozooids upon 

 the axial zooid is subject to great modifications, and affords the 

 principal character for the classification of the order. In the 

 Pennatuleae the autozooids are arranged in two bilateralh^ 

 disposed rows on the rachis, forming 

 the leaves or pinnae of the colony (Fig. 

 158). The number in each leaf in- 

 creases during the growth of the colony 

 by the addition of new zooids in regular 

 succession from the dorsal to the ventral 

 side of the rachis^ (Fig. 159). In 

 other Pennatulacea the autozooids are 

 arranged in rows which do not unite to 

 form leaves {Funiculina), in a tuft at 

 the extremity of a long peduncle 

 ( JJnibellula), scattered on the dorsal side 

 of the rachis {RenUla, Fig. 160), or 

 scattered on all sides of the rachis 

 {Cavernidaria, Fig. 161). In those 

 forms in which the autozooids are 

 scattered the bilateral symmetry of the 

 colony as a whole becomes obscured. 

 The siphonozooids may be found on the 



leaves {Ptevoeides), but more frequently between the leaves or 

 rows of autozooids, or scattered irregularly among the autozooids. 

 Usually the siphonozooids are of one kind only, but in Pen- 

 natula miirrayi there is one specially modified siphonozooid at 

 the base of each leaf,^ which appears to have some special but 

 unknown function. 



In UnibeUula gracilis each siphonozooid bears a single pinnate 

 tentacle, and in some other species of the same genus there is 

 a tentacle which is not pinnate.'' 



^ Jungersen {Danish Ingolf Exjtcdition, Pennatuliiia, 1904) l:as shown that tliis 

 is tlie correct nomenclature of the regions of the raciiis. Xearly all other autliors 

 describe the dorsal side as ventral and the ventral as dorsal. 



- S. J. Hickson, Report British Association (Southport Meeting), 1903, p. 688. 



•" ilarshall, Trans. Boy. Soc. Edinb. xxxii. 1883, \k 143. 



Fig. 159. — Diagram of a portiou 

 of a rachis of a Sea-pen. ant. 

 The rows of autozooids ; 1-6, 

 the order of age of the auto- 

 zooids composing a leaf ; D, 

 the dorsal side of the rachis ; 

 .SV, the siphonozooids ; T' the 

 ventral side of the rachis. 

 (After Jungersen.) 



