:ms,. j. j. SIMPSON ox isis iiiPL'tiRis. 421 



The Structure of Inis hi])]Juris^ LinntBus. By Jas. J. Simpson, 

 M.A., Niitural History DejiartmeiitjUuiversity of Aberdeen. 

 (Coummnicated by Pro!'. W. A. Hekdman, P.E.S., Pres.L.S.) 



[Eead 15tb Febniai-y, 1906.] 



(Plate 43.) 



The genus Isis was established by Linua?us in 1737 in his 

 ' Hortus Oliffortiauus,' p. 479, but he did not then include under 

 the generic appellation the species to which it was afterwards 

 applied. These he referred to the genus Sertularia. In his 

 ' Systema Naturaj,' ed. x. 1758, p. 1287, Linnaeus rearranged 

 his species, and placed in the genus Isis not only the species 

 referred to, but also all the Tsidinse, " le Corail " as well as the 

 Encrinites. Pallas, in his ' Elenchus Zoophytcrum,' 1766, 

 accepted the classification of Linnaeus and gave the following 

 generic description : — " Colony arborescent, sedentary ; axis 

 calcareous, porous with longitudinal striations, or jointed, bearing 

 a fleshy cortex ; verrucas sparsely scattered ; polyps flower- 

 shaped, oviparous, with a crown of tentacles, retractile." 

 Under this category he placed the following species : — I. nohilis, 

 I. dicliotoma, I. ocliracea, and I. liippuris. In 1786, Ellis & 

 Solander, in ' The Natural History of many curious and 

 unconnnon Zoophytes,' p. 105, defined the genus in the following 

 terms : — " An animal growing in the form of a plant whose stem 

 is stony and jointed ; the joints are furrowed longitudinally and 

 united together in some by a spongy, in others by a horny 

 substance. It is covered over by a soft porous and cellular 

 fiesli, full of little mouths from whence the polyps with their 

 claws come forth, through whom the eggs are produced." 

 They also noted the relationship between this genus and the 

 Gorgonids, a relationship based on the presence in both of 

 '•the axis, support or bone of the animal" ; the only difference 

 being the presence of joints in that of the genus under con- 

 sideration, while in the latter the axis is horny throughout. 

 They suggest that the "articulation" of the axis is an adaptation 

 for swaying in the water, flexing backwards and forwards in 

 the currents, and so minimising the possibilities of fracture. 

 To these eminent naturalists we are also indebted for the first 

 figures of any species of this genus, Tab. 3. figs. 1-5 repre- 

 senting various parts of I. liippuris, Linn. The only other species 

 described by them are I. ocliracea and I. coccinea. It is also to 



