ON THE D IP LO CHORDA. 415 



primarily from the mouth, the inverse to Dohrn's hypothesis, 

 which regards the Vertebrate mouth as a pair of fused 

 pharyngeal clefts, a view which does not appear to take suffi- 

 cient account of physiological differentiation. 



In part 1 (10) it was shown that Actinotrocha has five 

 coelomic cavities, with many of the relationships of the five 

 cavities in Balanoglossus ; and they were compared not 

 only with these, but with the five cavities which appear to be 

 an integral part of the constitution of a great number of the 

 lower Coelomata. In this last part of the work the origin of 

 these cavities is shown to be similar to that of the same 

 organs in Balanoglossus. 



Roule (15a) in a recent paper disagrees with my conclu- 

 sion on the relationship of Phoronis to the Heraichorda 

 (so called), and attempts to regard Actinotrocha as a 

 trochophore. The body-cavity of a trochophore is a 

 hgemocoele, whereas the hfemoccele is restricted in Actino- 

 trocha to small spaces between the ccelomic sacs. Until 

 Roule is in a position to demonstrate the absence of these 

 five coelomic sacs one need hardly attach much importance 

 to his comparisons of Actinotrocha with a trochophore 

 nor to his refusal to accept my enlignment of the former 

 with the Enteropneusta. 



St. Andrews; March, 1899. 



VOL. 43, PART 2. — NEW SERIES. F F 



