580 



INVEETEBEATA 



CHAP. 



greater size, but in the elaboration of the processes of its longitudinal 

 ciliated band. The sides of the prae-oral loop and of its outgrowths, 

 the prae-oral processes, as well as the sides of the main portion of the 

 longitudinal ciliated band and of its outgrowths, the antero-dorsal 

 processes, are fringed with small, secondary, finger-like processes. 

 There is also a second circular band of ciha behind the telotroch, but 

 much more feebly developed. According to Morgan, in this larva 



Fig. 424. — Longitudinal sagittal section through the New England Tornaria immediately 

 after its metamorphosis into the Balanoglossid worm. (After llorgan.) 



ajJ.n, nervous tissue underlying the apical plate ; ch, rudiment of notpchord ; coel, proboscis coelom ; 

 cof!^t collar coelom ; coe'^y trunk coelom ; mt, intestine ; n.p, dorsal neural plate in the collar region ; oes, 

 oesophagus ; p.col.g, posterior collar gi'oove ; st, stomach ; t.tr^ telotroch. 



the collar-cavities originate by the aggregation of scattered mesen- 

 chyme cells. This statement is in the highest degree improbable ; 

 such an impressidn might be produced on the mind of an observer if 

 the critical stages of the development were missed out. 



The principal additional points which Morgan made out satis- 

 factorily in these larvae were, the formation of the collar pores, and 

 the first traces of the genital organs. The collar pores originate 

 as two ectodermal invaginations situated on the sides of the body, not 

 far from the mid-dorsal line at the hinder region of the collar. The 



