EMBRYOLOGY OF THALASSEMA MELLITA 



211 



(oes.TTL.) 



Fig. 7. 



III. Fully Developed Trochophore. 



Between the twenty-fifth and thirtieth hours there is a rapid 

 increase in size of the trochophore, brought about by the 

 stretching and consequent thinning out of all the tissues. Conn 

 has described a similar swelling at the transition of the larva 

 into the adult, as has also Spengel ('79) in Bonellia. Conn {^^(i) 

 thinks that this is due to the absorption of water through the 

 anal vesicles as it takes place immediately after their formation. 



a. Ectoderm. — Since the difterentiations of the ectoderm have 

 been described in detail by Conn, they may be passed over 

 without extended comment. When the trochophores are 

 stained intra vitani with methyl blue or neutral red, certain 

 loosely arranged groups of granules (Text-Fig. 8, B) stain with 

 great intensity. These granules are present not only in the 

 body wall, but also in that of the gut and in some mesenchyme 

 muscles. It is questionable whether, as Conn ('86) maintains, 

 the absence of green granules is correlated with a lack of nutri- 

 ment. Hatschek ('81) concludes that the opposite is true, since, 



