240 



LOWER INVERTEBRATES. 



entoproctous Polyzoa, without a partition between the cell and the stalk, and with a 

 cement gland on the end of the stalk. The genus Loxosoma is represented in Euro- 

 pean waters by several species, distinguished, among other peculiarities, by the num- 

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

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

 as in other Polyzoa, become separated, and settle down to begin life for then;iselves. 



Sub-Class II. — Ectopeocta, 



This division, ■which contains by far the greater proportion of the Polyzoa, is far 

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

 is found in the fact that the anus is placed outside the circular or horseshoe-shaped 

 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. 



Order I. — GYMNOL JEMATA. 



The forms embraced in this order are almost wholly marine. They agree 

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

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

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

 larv£e leave the eggs as ciliated embryos, which swim freely for a time, and then settle 

 down to spend tlie remainder of their lives attached to some submerged object, fomi- 

 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 

 chitinous, 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. — Cyclostomata. 



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



which the mouth of the cell is round and un- 

 armed by spines, and in which, when the ani- 

 mal is retracted, the opening is not closed by 

 an operculum. Most of the genera and species 

 are extinct, yet many are found living in the 

 colder seas, the sub-order reaching its highest 

 development in Arctic waters. The living 

 fonns are arranged in six families, three of 

 which (CBisiADiE, DiASTOPOEiDiE, and Tubu- 

 LiPOBiD^) are represented 

 on the New England coast. 

 Crista eburnea, of which 

 we give enlarged figures, 

 is an ivory white, calca- 

 reous species, frequently 

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

 the cells are placed in rows, arranged transversely to the branches. Species of Tubu- 



Fio. 238. — Crisia eburnea. 



Fig. 239. —Idmcmea. 



