HIGH SCHOOL ZOOLOGY. 



239 



Lingtda, (a form with a long flexible peduncle, which can 

 displace laterally the upper valve of its shell owino- 

 to the absence of a hinge — Ecardines) the intestine 

 turns forwards and. opens near the mouth. Lingula 

 is an example of a " persistent " type, as the generic 

 characters do not appear to have altered from 

 F\s~Tm-L Palaeozoic times (Fig. 166). 



Levis^Torml- Although the adults are attached forms, the larvse 

 are free ; they are decidedly worm-like, being formed 

 of three segments, the hindmost of which becomes transformed 

 into the stalk, the foremost becomes much reduced, while the 

 middle one gives rise to the body and mantle-lobes. 



26, Like the Brachiopoda, the Polyzoa are bilateral animals, 

 sedentaiy in their adult condition ; they possess a circlet of tenta- 

 cles about the mouth, and are protected by a shell secreted by 

 the skin, but in other i-espects no resemblance is to be detected 

 between them, except during developmental stages. The fact 

 that the Polyzoa almost invariably form colonies by budding at 

 once sepai-ates them from the forms heretofore studied ; it is to 

 this peculiarity that the class owes its name. 



With the exception of Cristatella (Fig, 167), the colonies are 



permanently sedentary, being 

 attached by an extensive or 

 limited surface. According 

 to the relative position of the 

 buds they may be, in the 

 stem" of pond-weed. former case, massive, encrust- 



ing or straggling, in the latter, foliaceous or arborescent (Fig, 

 168). The moss-like form of the colonies has gained the class 

 the alternative name of Bryozoa. Each individual in the colony 

 secretes a " cell " into which the head with the crown of 



Fig, 167— Colony of Cristatella, attached to 



