320 GILBERT C. BOURNE. 



original position and to become more deeply situated. When 

 such cells form a layer situated between epiblast and hypo- 

 blast they constitute a third layer, a mesoblast. But in point 

 of fact we have no positive evidence that such a simple third 

 layer exists without the ancestral coexistence of a coelom. I 

 have already given reasons for believing that such a simple me- 

 soblast does not obtain in the Platyhelminthes. The nearest 

 approach to it is in the Ctenophora, and in them the stellate 

 cells are homologous^ not with the whole of the mesoblast of 

 the Ccelomata, but only with a part of it, viz. that part which 

 may be supposed to have originated independently of the 

 ccelom, but of the origin of which the traces are, in the 

 majority of cases, suppressed. 



The part is not the whole, nor should the name denoting the 

 whole be given to tbe part, for which reason I object to 

 giving the name mesoblast, or its equivalent mesoderm, to the 

 supporting lamina of Ccelenterata. I have proposed for it the 

 name Mesogloea, a name which was suggested to me by 

 Professor Lankester in the course of a conversation on this 

 subject, and which corresponds exactly to the Gallertlage of 

 German authors. Its meaning, '' middle jelly,^^ has particular 

 reference to the Medusae, of whose bodies it forms the greater 

 part. 



Before concluding this paper I have to express my obliga- 

 tions to Professor Moseley, who kindly permitted me to use 

 the Oxford laboratory during my studies, and assisted me with 

 much valuable advice. Also to my friends Mr. Hatchett 

 Jackson, and Mr. W. Baldwin Spencer of Oxford, who helped 

 me in many ways. 



