Cuming s — Development of some Paleozoic Bryozoa. 59 



The neanastic stage begins with the assumption of the habit 

 of budding that is to characterize the adult colony. In some 

 cases (Membranipora, Bugula, Aleyonidium) this takes 

 place very, early, the meta- and paranepiastic stages being 

 greatly abbreviated or entirely lacking. In other cases {Fenes- 

 tella) the adult habit of growth is frequently not suggested 

 until as many as fifty or sixty buds have been produced. The 

 neanastic stage terminates with the development of an adult 

 colony. 



The ephebastic and gerontastic stages refer, as in other 

 organisms, to fully adult and senile growths. The latter, espe- 

 cially, is marked by the extinction of the earlier polypides of 

 the colony and frequently by profuse deposits of secondary 

 sclerenchyma, as well as by other more or less extensive modifi- 

 cations affecting the basal portion of the zoarium. 



Phylastic Stage. 



The youngest observed specimens of Fenestella consist of 

 minute globular bodies (Hg. 45) of a diameter of about 0*l mm , 

 found upon the zoaria of Orthopora, Callopora, and other 

 Bryozoa of the Lower Helderberg (Shaly) limestone of Indian 

 Ladder, ]ST. Y. These minute bodies represent protoecia, and 

 have a definite aperture, but if the vestibule ever existed it 

 has been broken away. That they are the protoecia of Fenes- 

 tella is proved by their size relative to the zooecia of adult col- 

 onies of that genus, and by the very complete series (figs. 44- 

 46) of connecting stages, as well as by the presence of similar 

 bodies on the bases of adult Fenestella colonies. The young- 

 est individual figured (fig. 45, top) has already developed one 

 lateral bud. The protoecium may frequently be recognized by 

 its large size and significant position in the circle of zooecia 

 often to be seen on the base of well-preserved zoaria ; it can 

 be identified in transverse sections cutting the initial region of 

 the colony, and especially in transverse serial sections of this 

 region. Its exact relation to the primary buds has been 

 repeatedly demonstrated in serial sections of exceptionally pre- 

 served calcified material. The evidence bearing on this point 

 will be presented in a later paper. 



Nepiastic Stages. 



Ananepiastic Stage. — The initiation of this most interesting 

 and significant stage in Fenestella conforms to the general 

 plan that obtains throughout the Ectoprocta. It consists in 

 the formation of two lateral buds (figs. 44-46, I2, 1 3) and later 

 of a median bud (fig. 46, Ii). This order of budding has been 

 verified in numerous specimens of Fenestella from widely sep- 

 arated horizons and localities. The lateral buds originate in 



