BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 28. AFD. IV. N:0 7. 9 



hydrocoele. These outgrowths soon lose their connection with 



the coelora, and become converted into closed sacs The 



main body of the sac, however. forras a tooth-sac. From its 

 floor an npstanding projection is formed, which is the root 

 of the tooth, whilst from its sides the alveoli, which constitiite 

 the jaw, are formed. > 



In the meantime the -^^ectodermic disc» has undergone 

 several changes, a part of it having formed the »ncrve-ring» 

 with the yradial nerve-cordsy> and the centre having tnrned 

 inwards in order to form the y^ocsophafjus». At the same 

 period the nervöns system is evidently difierentiated into 

 threads and cells. 



A more complete account of the development of Echinus 

 miliaris may be given låter on. For the present the above 

 remarks may be sufficient. ^ 



' I had just finished this preliminary account when I received the last 

 nuniber of Johns Hopkins university Circulars (Vol. XXI. No. 157. Baltimore, 

 April, 1902) where Caswell Grave has published: »Some points in the structure 

 and development of Mellita testudinata». 



