240 



L WER rX VER TEBR A TES. 



eiitoproetoiis Polyzoii, without u partition ht'twueii tbe cell and the stalk, and with a 

 cement gland on the end of the stalk. The genus Loxosoma is represented in Eui'o- 

 pean waters by several species, distinguished, among other jieculiarities, by tlie num- 

 ber of tentacles. These forms attach themselves to sertulavian« and other Polyzoa, 

 and reproduce by budding. These buds, instead of remaining attached to the parent 

 as in other Polyzoa, become sejiarated, .and settle down to begin life for themselves. 



Sub-Class II. — Ectoprocta. 



This division, which contains by far the greater pro]tortion of the Polyzoa, is far 

 more complicated in its structure than the Entoprocta. A most important distinction 

 is found in the fact that the anus is placed outside the circular or liorseshoe-sliaped 

 ring of tentacles. There is further a tentacular sheath. Other characters will be 

 noticed in our subsequent account of the two orders into which the sub-class is 

 divided. 



Ordeu I. — GYMN( )LyEMATA. 



The forms embraced in this older are almost wholl}' marine. They agi-ee 

 in having the ring of tentacles in a complete circle and in the absence of a 

 lophojihore, a structure which will be mentioned when treating of the other order. 

 Statoblasts are but rarely jiresent (as in the fresh-water genus Paludicella.) The 

 larviE leave tlie eggs as ciliated embryos, which swim freely for a time, and then settle 

 down to spend the remainder of their lives attached to some submerged object, form- 

 ing a colony by the process of budding. In the shape and constitution of the external 

 skeleton the greatest diversity exists, it being sometimes calcareous, sometimes 

 chitiuous, and at others gelatinous. The order is divided into three sub-orders, 

 founded upon the shape and ornamentation of the mouth of the cell containing the 

 polypide. 



Sub-Order I. — C'ycl(isto.mata. 

 The cyclostomatous Polyzoa, as is indicated by the name, embraces those forms in 



which the mouth of the cell is round and un- 

 armed by sjiines, and in which, Avhen the ani- 

 mal is retracted, the opening is not closed l)v 

 an operculum. Most of the genera and S])ecies 

 are extinct, yet many are found living in the. 

 colder seas, the sub-order reaching its highest 

 develo])ment in Arctic waters. The living 

 forms are arranged in six families, three of 

 which (Crisiad.e, DiASTOPORiDyE, and Tueu- 

 lipohid.e) are represented 

 on the New England coast. 

 Crisia eburnea^ of which 

 we give enlarged figures, 

 is an ivory white, calca- 

 reous sjiecies, frequently 

 found attached to seaweeds in tide-pools and in deeper water. In the Tubulipoi-idaj 

 the cells are placed in rows, ai'ranged transversely to the branches. Species of Tiihu- 



