ZOOPHYTA BRITANNICA. 



ORDER IV. 



Z. ASCIDIOIDA. * 



Character. 

 Polt/pes aggregate^ the mouth encircled with filiform ciliated 

 retractile tentacula ; a distinct stomach, with a curved intestine 

 terminating in an anus near the mouth ; ova internal. — Polypi- 

 dams very variable, — either horny fistidar and confervoid, or cal- 

 careous, membranous, or fibro-gelatinous, formed of cells connected 

 and arranged in a determinate and usually quincuncial manner. 



Observations. 

 In the preceding orders we found reason to conclude that 

 the polypidom of the Hydroida was a sheath disconnected, or 

 at least not in organic union, with the soft pulpous matter which 

 it invests and protects ; that the corresponding part in the Aste- 

 roida, become an interior siieleton or axis, held the same rela- 

 tion to itspolypiferous crust; nor was this relation altered when 

 the polypidom had again, in the Helianthoida, assumed an ex- 

 ternal position, forming an integral part of the epidermis. In 

 all these instances the polypidom. appears to be unorganized, 

 and when once formed, beyond the reach of change from either 

 the polypes or its own inherent powers ; -f- but in the present 



* This order corresponds with the Polyzoa of Thompson, the Bryozoa of 

 Ehrenberg, the Bryozoaires of Milne- Edwards, and the Ciliobrachiata of 

 Farre. Our order Hydroida Farre designates Nudierachiata, thereby indicat- 

 ing the absence of cilia on the tentacula ; aiid Milne- Edwards les Sertulai- 

 RiENS. His Alcy'oniens is synonymous with our Asteroida ; and the Zoan- 

 taires with Helianthoida, but Farre unites these under the name of Antho- 

 ZOA, borrowed from Ehrenberg. 



•\- " Unorganized non-vascular parts are produced by an organized matrix, 

 and grow by the continued deposition of new matter on one surface." Miiller's 

 Elements of Physiology, p. 384. 



