250 



PHYLUM ANNELIDA. 



(a) Tentacles in a crescent Fresh water, Cristatella, Lophopus, etc. 



(b) Tentacles in a circle Marine, except Paludicella ; Flustra, the 

 common sea-mat ; Membranipora^ encrusting seaweed, etc. ; Cellepora, 

 very calcareous ; Alcyonidium^ gelatinous. 



The Entoprocta include the colonial Pedicellina, with a few allied 

 genera, also the non-colonial Loxosoma, in which the buds separate 

 as soon as they are formed. All the forms are stalked and minute. 

 The anus is included within the tentacular circle. In the meta- 



M 



FIG. 129. Diagram of an Ectoproctous Polyzoon 

 (Plumatella}. 



L., Lophophore ; PH., pharynx; A., anus; S., stomach; 

 M. } retractor muscle ; F., funiculus, a cord of mesodermic 

 tissue; 0., cells that form "statoblast" buds; B., an 

 ordinary bud; ., epistome over the mouth; T., tent- 

 acles ; S&., outer wall of zooeciura. 



morphosis of Pedicellina there is an elongation of the dorsal region of 

 the body, and a consequent approximation of the mouth and anus on 

 the shortened ventral surface. There is no apparent body cavity in the 

 adult, and the mesoderm arises from two primitive mesoblasts. The 

 nephridia are anterior, minute, and do not serve as genital ducts, but 

 resemble the " head kidneys " of Annelid trochospheres. They are said 

 to terminate in flame-cells like those of Platyhelminths. In all these 

 three respects the Entoprocta differ from the Ectoprocta, and from the 

 Molluscoidea generally. 



