38 THE POLYPI. $$ 25, 26. 
Van Beneden. Recherches sur l’Anatomie, la Physiologie et le devel- 
oppement des Bryozoaires. Mém. Acad. Brux. Tomes XVIII. XIX. 
Recherches sur les Bryozoaires fluviatiles de Belgique. Ibid. Tom. XXI. 
For further literature on the Bryozoa, see the writings quoted _ my 
notes, and especially those of Aliman. D. 
CHAPTER I. 
CUTANEOUS ENVELOPE AND SKELETON. 
§ 25. 
The Polypi are composed of either entirely soft parts,” or have for their 
support a solid frame, which may he 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 polypary, is‘ formed partly internally, and partly externally, by 
these animals. In the first case it is called an azial, 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. When, 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 df 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. 
2 Corallium. 
3 The Gorgonina. 
4 These corpuscles are easily seen in Alcyonium 
and Lobularia. (Milne Edwards, Anon. d. Sc. 
Nat., Zool. IV. 1835, pl. XIII. fig. 9; Pl. XV. fig. 
10-11.) Spicula of this kind are found in the 
interior of their tissues, as well as on the surface. 
Ehrenberg (Abhand. d. Berl. Akad. 1841, Th. I. 
*It should here be remarked that the old, and 
as now regarded, mistaken view of the formation of 
the frame of Polyps is here repeated; for the frame 
4g generally an internal skeleton, as. for instance, 
p. 403, Taf. I.-III.) has described and figured these. 
spicula under the names of Spongolitkis and. 
Lithostylidium. 
5 The Madreporina. 
6 Millepora, Madrepora, Oculina and Astraeae 
? Gorgonia, Isis and Corallium. 
8 The Actiniae. 
9 Eschara and Cellepora. 
with Madrepora, Astraea, &c. For the formation: 
of Coral, see Dana, loc. cit.; and for the relations of 
the corallium carried out in detail, see Edwards and 
Haime, Ann. d. Sc. Nat. 1849, ’50, 51. — Ep. 
