1908] Davis. — Life-history of Dolichoglossus. 215 



If we are looking for types having a development of body 

 cavities similar to that found in D. pusiJlus we must take into 

 consideration Annelids and Molluscs. In both of these groups 

 the general plan of mesodermal development as shown, for ex- 

 ample, by Wilson, for Annelids and by Conklin for Molluscs may 

 be briefly stated as follows: The development of body cavities is 

 from in front backwards. The mesodermal bands posterior to 

 cavities already formed are undifferentiated and "new cell ma- 

 terial continues to be formed here in the vicinity of the primitive 

 mesoderm cells. ' ' 



The development of the body cavities in D. piisillus, as I have 

 shown, follows in a very general way the above plan. But I do 

 not wish in making this comparison to suggest any homology. 

 On the contrary, I wish rather to emphasize the great difl^cv^lty 

 in the present state of our knowledge of establishing any homo- 

 logies whatever for these structures. 



