150 



EMBRYOLOGY 



Fig. 71. — Embryo of Callianira 

 bialata viewed from above (after 

 Metschnikoff). r, ciliary plates ; 

 t, fundament of the tentacular ap- 

 paratus ; m, cruciform mesodermal 

 fundament ; g, migratory cells in 

 the mesoglcea. 



muscle fibres were secondarily to sink into the mesoderm, nothing in the 

 real nature of the gelatinous tissue would be changed by this. 



In order to explain the presence of 

 four mesodermal bands, Kleinenberg 

 (Literature Annelida, i., No. 26, p. 13) 

 IJerceives in them an indication of the 

 existence of four tentacles (two lateral 

 and two sagittal) in the ancestral forms 

 of the Ctenoiihora, of which those in 

 the sagittal plane have become de- 

 generated. It is interesting to know 

 that in the Beroidse, which are with- 

 out tentacles, there exists an entirely 

 similar mesodermal fundament, which 

 extends in the transverse direction at 

 the apical pole, and there comes to lie 

 under two ectodermal thickenings 

 (rudiments of tentacles) (Metschni- 

 koff). The further fate of this meso- 

 dermal fundament 

 could not be followed. 



As regards the 

 formation of the 

 sexual organs, 

 which does not 

 fall within the 

 period of embry- 

 onic development, 

 but occurs in later 

 stages, R. Hertwig 

 has shown by his 

 observations on 

 Callianii-a that it 

 is probable that 

 they are of ecto- 

 dermal origin. 

 The sexual pro- 

 ducts, to be sure, 

 ripen directly un- 

 der the epithelium 



— wp 



Fig. 72. — Young larva of Callianira bialata (after 

 KowALKvsKY, from Hatschkk's Lehrhuch). t, tenta- 

 cles ; ot, auditory organ ; so, apical organ ; wp, the 

 rows of ciliary plates; en, the four entodermal sacs; 

 «, CESophagup. 



