354 ZOOLOGY SECT. 



represented in the Cambrian and later Palaeozoic formations by 

 forms which appear to have belonged mainly, if not exclusively, 

 to the Cyclostomata. In the later formations of the Mesozoic period 

 the Cheilostomata are also abundantly represented, and in the 

 Tertiary the latter sub-order greatly outnumbers the Cyclostomata. 

 The Tertiary Polyzoa flourished in certain localities in such 

 luxuriance that their remains form calcareous deposits of very 

 great extent. 



Sub-Class II. — Endoprocta. 



While the sub-class of the Ectoprocta comprises a large number 

 of genera, that of the Endoprocta includes only Pedicellina (Fig. 283), 

 Loxosoma, Urnatdla, Myosoma, Gonopodaria and Ascopodaria, with 

 one or two other less completely known forms. They are all 

 marine except Urnatella — an American fresh-water genus. The 

 feature indicated by the name of the sub-class — viz. the position 

 of the anus within the circlet of the tentacles, is an important 

 point of difference from the rest of the class ; but there are others 

 of as great or greater importance. 



In none of the Endoprocta is there is a distinct introvert. The 

 body is cup-shaped, with a rim which is capable of being inverted 

 over a cavity — ^the vestibule — within which the tentacles can be 

 withdrawn, and which contains both mouth and anus. An epistome 

 overhangs the mouth. The coelome 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 hyahne 

 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 (Fig. 283, gang), situated between mouth 

 and anus as in the Ectoprocta, is bilobed in Loxosoma. Testes 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. 



Pedicellina and Urnatella are colonial, Loxosoma solitary. In 

 Pedicellina (Fig. 283) there is a creeping stolon with which a 

 number of zooids are connected ; a diaphragm separates the body 

 of each zooid from the stalk. Gonopodaria ramosa has a branching 

 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 body 

 and the stalk. In the base of the latter is the so-c&Wed foot-gland, 

 consisting of a small number of granular cells arranged around a 

 central space opening on the exterior. Buds are formed, but 



