160 Descriptio7is of Preparations. 



For the anatomy of the Actiniae, see Hollard, Ann, Sci. Nat., 



Ser. iii., torn, xv., 1851, p. 257; Huxley, Med. Times, June, 



1856. 

 For a zoological description of Actinia Crassicomis, see Johnston, 



British Zoophytes, 1847, 2nd edition, p. 226. 

 For the anatomy and morpholog-y of the entire sub-kingdom 



Coelenterata, see Greeners Mantial of the sub-kingdom Coe- 



lenterata, 1861. 

 For the points of distinction between the Coelenterata and the 



Echinodermata, see Van Beneden, Recherches sur la Faune 



Littorale de Belgique Polypes, 1866, pp. 55-62. 



48. Sea-Fir {Sertidaria Ahietina). 



A COMPOUND Hydroid Polype, plant-like in form, and differing 

 from the preceding specimen in being fixed to one spot in adult 

 life, and from the entire class to which the Sea-Anemones belong, 

 by the much smaller size and simpler structure of each of its 

 constituent zooids. The specimen consists of a number of regu- 

 larly branched stems, which arise near to each other from a 

 creeping stolon ; and are beset by series of closely arranged subal- 

 ternate cells, the ' hydrothecae^ containing the zooids. In the 

 upper half of the specimen, the main stems and the pinnae may 

 be observed to carry, besides the regularly arranged hydrothecae, 

 certain larger cells, irregularly arranged along their upper surfaces. 

 These latter cells are the ^gonophores^ of Hincks, the ^teleophores^ 

 of Van Beneden ; they differ from the other cells or hydrothecae, 

 in that their contents are the sexual products developed within 

 processes of the 'coenosare,^ which possess neither the digestive 

 cavity nor the prehensile tentacles of the smaller hydrothecae. 

 Appended to the apices of some gonophores, may be seen the 

 marsupial pouch, into which the ova are transferred at a certain 

 stage of their development. The gonozooids, or the contents of 

 the gonophores, we may call *^medusiform buds,' but they never 

 in the family Sertulariidae take the shape of Medusae. The em- 

 bryos are at first spheroids richly covered with cilia ; subsequently 



