Chap. IV.] 



ANTHOZOA. 



in 



channelling the surrounding tissue, but rather of a 

 series of chambers separated from one another by nar- 

 row septa, while even these are perforated by two 

 holes (Fig. 54 ; I). 



The mouth is an elongated slit, which sometimes 

 becomes constricted in its middle, so that we have 

 essentially two orifices. 

 On the ventral side of this 

 slit a groove is often deve- 

 loped, which leads into the 

 gastric cavity ; the cells 

 which line the sides of 

 this groove (the " siphono- 

 glyphe " of Hickson) (Fig. 

 55 ; st), are ciliated, and by 

 the action of these cilia 

 the food is carried to the 

 digestive region of the 

 body ; the presence of this 

 groove or the size to which 

 it is developed have been 

 observed to vary with the 

 size of the animal, or of 

 the colony of which the 

 polyp is a part; or, 



Fig. 54. Section of Saga rtia 

 parasitica. 



t, Tentacle ; I, internal septal stoma ; 

 Im, longitudinal muscle ; tm, trans- 

 verse muscle ; pm, parietal mus- 

 cle ; v, mesenterial filaments ; w, 

 Acontia. (After O. and R. Hertwig.) 



Ill 



other words, to depend upon the demand for food 

 which is made by the Alcyonarian (Fig. 55). 



The great size of this mouth slit, and the fact that 

 it is often constricted in its middle, are of considerable 

 importance as bearing on the early history and func- 

 tion of the blastopore, or opening into the gastrula ; 

 in simple or archaic forms, such as Peripatus, the 

 blastopore is a greatly elongated slit which closes up 

 in the middle, and forms the mouth at one end and 

 the anus at the other. 



In the Anthozoon Peachia the mouth slit is 

 similarly converted into two openings, one of which 



