488 POLYZOA 



The commonest Entoproctous genus is Pedicellina, a graceful 

 little animal, which occurs on many parts of our coast. It may 

 often be discovered by looking carefully on the pink, jointed, 

 calcareous alga, Corallina, which may be found growing at the 

 edges of deep and cool rock-pools not too far above low-water 

 mark. Its creeping stem or " stolon " is firmly attached to the sur- 

 face of the seaweed, and sends off vertical stems here and there. 1 

 Each stem bears a " calyx," which is practically an individual of 

 the colony. The stolon terminates, at one or both ends, in a 

 growing-point {a), from which new individuals are budded off. 

 The stalks bend from time to time in a curious spasmodic manner, 

 by which means the calyces are moved about with an irritable 

 and angry air. A good idea of the way in which the tentacles 

 are folded away when the animal is disturbed may be obtained 

 by putting the two wrists together, with the fingers spread out 

 to represent the tentacles, the retraction of which would be repre- 

 sented by turning the tips of the fingers down into the space, the 

 " vestibule," between the two palms. A delicate fold of skin 

 growing from the edge of the calyx closes over the retracted 

 tentacles, owing to the contraction of a sphincter muscle present 

 in its circular edge. The body-wall is not separated from the 

 alimentary canal by a definite body-cavity, so that there is no 

 obvious distinction between the polypide and the zooecium. The 

 existence of the Entoprocta is in fact a strong reason for refusing 

 to admit that these two terms correspond with two different 

 kinds of individuals. 



Let us now imagine the condition we should have if a large 

 and continuous cavity were developed between the alimentary 

 canal and the body-wall. The body-wall would clearly have the 

 general relations of a zooecium, while the alimentary canal and 

 tentacles would obviously correspond with the polypide. The 

 existence of the body-cavity would make it possible for the animal 

 to retract its tentacles instead of merely turning them in. Ee- 

 garcled in this way, there is but little difficulty in comparing the 

 Ectoprocta with the Entoprocta. 



The calyces are deciduous, i.e. they are lost from time to 

 time, the end of the stalk then producing a polypide-bud, which 



1 Barentsia Hincks ( Ascopodaria Busk) differs from Pedicellina in that each 

 stem has a muscular swelling at its base. The genus is represented by two British 

 species, B. gracilis Sars and B. nodosa Lonias. 



