23V> 



spriiii;-. Then, under the influence of the warmth, tlie statohiast hatches with its 

 organs ah-eady well developed. At first it swims freely through the Wciter, but soon 

 it becomes attached to some submerged object, with which henceforth its fortunes are 

 insejjarably united. It now develops its cajisule, and soon a bud is seen upon one side, 

 which eventually grows into an individual, undistinguishablo from the parent. Tiiis 

 process is again and again repeated, until a large colony is formed, either extending 

 its branches like a tree, or incrusting some submerged object with a gelatinous or cal- 

 careous envelope, forming in some instances clusters several feet in diameter and 

 eight or more instances in thickness. This same pi-ocess 

 of budding takes place in the marine genera. 



We do not yet know enough about the develo])ment 

 of the eggs of the Polyzoa to reconcile all the widely dif- 

 ferent features of the embryology. Still, all the various 

 forms of larv£e may be reduced to a body surrounded by 

 a ring of cilia (possil)ly corresjionding to the lophophore), 

 which divides it into two faces. On one of these is the mouth, and in some the anus 

 also. On the other is a ciliated disc, by which, it may be, the animal attaches itself. 



The Polyzoa first appear in time in the silurian rocks, and have persisted to the 

 present day. The oldest forms known ai-e referable to groups now living. At one 

 time it was thought that the gra]it()lites miglit belong here, but now the best authori- 

 ties are inclined to ]ilace them among the hydroids 



I of Atcyoviifinii 



Sub-Class T. — Entopkocta. 



The jirimary feature characterizing this grou]) is the position of the vent, which is 

 placed within the circle of tentacles, thus indicating that the group is the lowest of 

 the sub-classes, a feature which is characteristic of the larvte of some of the higher 

 groups here persisting in the adult, as can be seen by comparing the figure of Cyj^ho- 



nautes (fig. 246), which is the larva of Membrani- 

 pora, with that illustrating the anatomy of the adult 

 Pedicelliria (fig. 237). In this groM]i the tentacles 

 are not retractile, but can be rolled u]). 



In the Pedicellinid.e there is a creeping root- 

 stock, from which at intervals the long-stalked indi- 

 viduals arise and the colony increases by budding. 

 On our coasts is found PedicelUna americana, which 

 creejis over other Polj'zoa, hydroids, etc., forming 

 snnill white branching stems, the stalked individuals 

 resembling so many clubs. Uruatella is a fresh- 

 wa,ter genus, represented, so far as is at present 

 known, by only a single species, Urnatdla (/racilis, 

 from the Schuylkill River at Philadelphia. In this 

 brightly colored form the cells are borne on the ex- 

 tremities of long noded branching stalks. • In former years the species was very abun- 

 dant just below the dam whicli supplies the city of Philadelphia with water, but now, 

 doubtless owing to the pollution of the river by sewage, specimens are but rarely 

 found. 



The LoxosoMiD^, which were first made known in 18G3, are long-stalked, solitary 



V\r,. 237. — Anatomy of /^edicefUua ; 

 blooil pouuli; )H, montli; 7(, ganglion 

 rectum; s, stomach; /, tentacles. 



