88 THE POLYPI. §§ 25, 26. 



Yan Beneden. Recherches sur I'Anatomie, la Physiologie et Ic devel- 

 oppeinent des Bryozoaires. Mem. Acad. Brux. Tomes XVIII. XIX. 



Recherches sur Ics Bryozoaires fluviatilesdcBelgique. Ibid. Tom. XXI. 



For further literature on the ]Jryozoa, see the writings quoted in my 

 notes, and especially those of Allman. Ed. 



CHAPTER I. 



CUTANEOUS ENVELOPE AND SKELETON. 



§ 25. 



The Polypi arc composed of either entirely soft parts, ^' or have for their 

 support a solid frame, which may be calcareous, corneous, or coriaceous. 

 This frame is always the product of the general skin, and ought therefore 

 to be compared to a cutaneous skeleton."* This skeleton, known by the 

 name of polyparij, is formed partly internally, and partly externally, by 

 these animals. In the first case it is called an axial, and in the second a 

 tubular polypary. 



The axial polypary consists, with some polyps,*-' of a dense substance, 

 apparently unorganized and composed of carbonate of lime; with others,'^' 

 of a corneous substance, equally unorganized. When the polypary is 

 coriaceous, it is often covered by a variable number of calcareous, fusiform 

 corpuscles, usually bossed or dentated.*^' With some calcareous polyparies *^' 

 this is also true, and then the corpuscles are arranged in compact reticu- 

 lated masses. The tubular polyparies serve as a refuge for the animals 

 living in them, and in many cases, being common to many individuals, 

 these last are in direct relation to each other by the canals which traverse 

 the branching tubes. In the axial polyparies there are often cavities or 

 depressions of a variable size,**'' in which the animals can conceal them- 

 selves. AVhen, however, these are wanting,*'' they retire, as is the case 

 with many soft polyps,**" beneath their mantle. Sometimes,*"' these cavities 

 are closed by a movable operculum. 



§ 26. 



The skin of polyps is very transparent, and should be carefully dis- 

 tinguished from the parenchyma which it envelops. It is smooth, or it is 

 covered with ciliated epithelium. And, since it has been shown that many 



1 The Actinina and Hydrina. p. 403, Taf. I.-III.) has described and figured these 



2 CoTattium. "- spicula under the names of Sponsotithis and 



3 The Gorgonina. Lithostylidium. 



* These corpuscles are easily seen in Alcyonium ^> The .Madreporina. 



and Lobularia. (Milne Eiiward.i, Ann. d. Sc. >J Mi/lepora, Madrepora, Oculinaznd Astraea. 



Nat., Zool. IV. 18:i5, pi. XIII. fig. 9 ; PI. XV. fig. 'i Gor^onia, Isis and Corallium. 



10—11.) Spicula of this kind are found in the S The Actiniae. 



interior of their tissues, as well as on the surface. 9 Eschara and Cellepora. 



Ehrenberg (Abhand. d. Berl. Akad. 1841, Th. I. 



* It should here be remarked that the old, and with Madrepora, Jstraea, ifC. For the formation 

 as now regarded, mistaken view of the formation of of Coral, see Dana., loc. cit.; and for the relations of 

 the frame of Polyps is here repeated ; for the frame the corallium carried out in detail, see Edwards and 

 l8 generally an internal skeleton, as, for instance, liaime, Ann. d. Sc. Nat. 1849, '50, '51. — Ed. 



