ENDOPROCTA. 



77 



The Bryozoa are for the most part marine, and they attach them- 

 selves to stones, Lamellibranch shells, corals and plants. Some 

 fresh-water forms belonging to the genus Cristatella have the power 

 of moving about. 



The Bryozoa were widely distributed in the earlier periods, as 

 their numerous fossil remains, which increase in number from the 

 Jurassic period onwards, prove. 



Order 1. ENDOPROCTA.* 

 Bryozoa with anus within the circle of tentacles. 



In the structure of their bodies and the formation of their colonies 



Ms 



FIG. 551 Development of Pedicellina echinata (after B. Hatschek). a, Blastosphere with 

 flattened side of endoderm. EC, Ectoderm; En, endoderm ; Fh, segmentation cavity. 

 b, Later stage in optical median section. One of the two first mesoderm cells (Ms) which lie 

 to the right and left of the middle line is indicated, c, Later stage in optical median section. 

 Dr, Cement gland ; Oe, oesophagus ; Af, first rudiment of the rectum. d, Young larva in 

 optical median section. A. Atrium ; HD, rectum ; Kn, bud. c, Free-Swimming larva, 

 extended. N, Excretory canal ; L, liver cells ; Ms, mesoderm cells. 



the Endoprocta present simpler, more primitive conditions since they 

 retain essentially the organization of the Bryozoan larva. The 

 tentacular apparatus of the adult is from its origin directly re- 

 ducible to the ciliated crown of the larva. Mouth and anus both 

 open within the tentacular circlet into a kind of atrium, which forms 



* Besides Nitsche, cf., B. Hatschek, " Embryonal Entvvickelungund Knospung 

 der Pedicellina echinata." Zeit.fur miss. Zool., Tom. XXVIIT. 



