30 AKT. 1. — T. FIJJJTA : ON THE FORMATION 



or Hecoudarv mesoblaHt " is often ck'sciibed tis boiiii;; foi'incd iVoiii 

 one or otlier of the ectoderm-cells, and it is sm)posed to contril)ute 

 toward the foruiation of the niesencliynie. In the present species 

 I was not able to lind any trace of it so far as the investigation 

 extended. 



Several years have elapsed since I carried ont the alnjve 

 investigation, and during that period, tlie investigations by 

 WiEKZEjsKr, Meisenheimer, Heath, Holmes, Cauazzi, Geor- 

 GEWiTCH etc. on similar subjects have been published. Generally 

 s})eaking, they have tended to confirm and verify the pro2)Osition« 

 that had already been made known by previous authors. I con- 

 sider it advisable to refer to some of these works which bear 

 directly on what I have described above. 



In January 1900 there appeared a paper on the development 

 of Aplijsla liiiiacina by Carazzi, and again eight months after 

 another paper by George witch on A. dep'dans. 



Carazzi has carefully traced out all the developmental 

 processes up to the formation of the mesoderm-layer noting the 

 time exactly. When we compare his results with those given 

 above, it will be seen that they agree in the main. Nevertheless, 

 there are discrepancies on some important points which cannot 

 l)e ])assed without a word. The difterentiation of the germ-layers 

 in general is reached a little earlier in our species than in that 

 studied by the Italian author, excepting the formation of the 

 (iitomei'e />,, whicli is far earlier in his sj^ecies. In his Fig. 

 2 we see the illustration of an egg from its apical pole, 

 whicli coincides with Fig. 53 of the present pa[)er. But one of 



