VIII 



PHYLUM MOLLUSCOIDA 



327 



overhangs the mouth. The coetome is almost or quite obliterated, 

 the space between the alimentary canal and the wall of the body 

 being filled, more or less completely, with a gelatinous hyaline 

 matrix. A pair of nephridia are present. In Loxosoma they lie 

 one on each side of the oesophagus and open separately on the 

 exterior: they are ciliated intra-cellular tubes, each of which 

 probably begins in a flame cell. In Urnatella the two nephridial 

 tubes unite to open into the cloaca a diverticulum of the 

 vestibule. The ganglion (gang), situated between mouth and anus 

 as in the Ectoprocta, is bilobed in Loxosoma. Tcstes and ovaries 

 occur in the same individual in some, but appear to mature at 

 different times : they are provided with special ducts ; in others 

 the sexes are separate. 



Peclicellina and Urnatella are colonial, Loxosoma solitary. In 

 Pedicellina (Fig. 260) there is a creeping stolon with which a 



tent 



FIG. 200. Pedicellina. Showing successive stages -(numbered 1 to 6) in the development of 

 zooids by budding, an. anus ; gang, ganglion ; mo. mouth ; tent, tentacles (retracted). (After 

 Hatschek.) 



number of zooids are connected ; a diaphragm separates the body 

 of each zooid from the stalk. Urnatella has a disc of attachment 

 with one to six, jointed, branching stems. In Loxosoma, which is 

 found attached to various Annulata, two parts are distinguishable 

 the calyx or l)ody and the stalk. In the base of the latter is the 

 so-called fool-gland, consisting of a small number of granular cells 

 arranged around a central space opening on the exterior. Buds 

 are formed, but become detached before reaching maturity. Seg- 

 mentation of the ovum is complete, and a gastrula is formed by 

 invagination. 



