MUSEUM OF COMPARATIVE ZOOLOGY. 127 



certain germ layer, can assume the task of building organs in budded 

 individuals similar to those derived from a different layer in the sex- 

 ually produced individual. 



Whatever may be the truth of the conclusions reached by Haddon 

 ('83, pp. 548, 549, 552) and by Joliet ('86, pp. 54-56), that the nervous 

 system and the alimentary tract arise from two distinct layers, or kinds 

 of cells, in the species studied by them (and their evidence is certainly 

 not conclusive even for these), their attempts (Haddon, '83, p. 540, 

 Joliet, ? 86, p. 57) to apply their results to the Phylactolaemata are not 

 justified by the observations which are here presented, nor by those 

 which have been made upon most Gymnolsemata and Endoprocta. 



4. Origin of the Alimentary Tract. — There is a curious difference 

 between the Endoprocta and the Ectoprocta in the development of the 

 organs of digestion. Seeliger ('89, pp. 182-184) has shown for Pedi- 

 cellina, that the oesophagus and stomach arise as an e vagi nation of 

 the oral wall of the young bud, which secondarily becomes connected 

 with the proctodeum. Haddon ( ? 83, pp. 517, 518) has shown for 

 Flustra, Barrois ('86, pp. 73-86) for Lepralia, Braem ( r 89 b , pp. 677, 678) 

 for the statoblast polypides of Cristatella, and the present paper for the 

 polypides in the adult Cristatella, that the oesophagus only is formed 

 on the oral side, the stomach arising with the rectum on the anal side 

 of the atrium. In all cases the oesophagus is formed first (Plate II. 

 Fig. 13). A comparison of my Figure 18 with Figure 41, Plate XXX., 

 of Hatschek ('77), shows a striking resemblance between the two. The 

 form of the alimentary tract and the depression to form the ganglion 

 are practically identical ; and were the tentacles to arise directly from 

 the immature lophophore arm (br. loph., Fig. 18), and from the circum- 

 oral fold which has already appeared, it would be difficult to decide 

 whether the anus opened outside or inside the circlet of tentacles, — 

 whether, at this stage, the Cristatella polypide were ectoproct or 

 endoproct. 



5. Origin of the Central Nervous System. — The only observations on 

 the origin of the brain in Bryozoa relate to Phylactolaemata and Endo- 

 procta. In buds of Pedicellina, the ganglion is formed, according to 

 Hatschek ('77, p. 520), as an invagination of the floor of the atrium, 

 which later becomes cut off as a hollow sac. Harmer ('85, pp. 274, 275) 

 has studied the origin of the ganglion in the bud in Loxosoma. He 

 states that it is derived from the floor of the vestibular [atrial] cavity, 

 and (apparently on purely theoretical grounds) that this latter is ecto- 

 dermic. " In a longitudinal section through a fairly advanced bud 



