ü2S I. IKEDA : 



Houle ('90) al^o dinliiiguislied two s(H't.s of mcsoblabt cells in 

 view of tlieir different origin and fate : '' Meseneliynies primaires " 

 and '* initales niésoderniiqnes." Both are derived from the " pro- 

 toendoderme" whieh foi'ins the primaiy arehenterie wall. The 

 lattcu' gives rise to cells grou})ed together into two compact 

 " bandlettes mésodermiques," Avhich are regarded as homologous with 

 the mesodermal l)ands of Annelid larvœ. In reality these hands 

 are, as have been pointed out by Sciiultze, nothing else tlian the 

 posterior ])aired diverticula of Caldwell. 



From the account of the mesoblast-formation given in the 

 foregoing lines, it is evident that the first stages of that process 

 are observable from the vei'v Ijeginning of gastrulation (ligs. 2(] a 

 & b), and long before the l)lastopore takes the small triangular 

 sha})e. ( )n this j)oint my observations stand at variance with 

 Caldwell's. Nor can I agree with that author in the o}>inion 

 that the mesoblast produced from the auterior diverticula (even 

 thouL!:h consisting of onlv two or three cells) incloses an enterocudic 

 cavity. As already described, the cells in question, after l)eing 

 bud(h'd oil', lie loose in the blastocœle together with jU'eexisting 

 mesoblast cells and without forming a wall to a special cavity of 

 any sort. 



As to the ventral groove, Metsciinikoff ('82) was tlie fust 

 to refer to this structure and wrote as follows : " In pd.^seiuler 

 Lage dc6 Kmhryo^ Icann man cine in Verbindung mit detii Bla^to- 

 porus beßndliehen FurcJte {/ongiéiidina/e) waln'nehinei), (reiche zum 

 Tliniercnde des Embryox hinzieht und sich nur auf dein Ehtodenii' 

 beshränlct. Diese Furclie erhöht den bilateralen Bauplan des 

 Embryos erscheint indessen als eine vergängliche Bildung, welche 

 man auf sjnUeren Stadiunh rergebens suchen vAlrde'''' {I.e., p. oOl). 

 According to Caldwell, this groove, which he calls " the primi- 



