GENERAL ZOOLOGICAL POSITION. 



Ccelomate Metazoa, which do not retain the radial 

 symmetry of the gastrula. In their germinal layers and in 

 their internal cavity they differ so much from Coelentera and 

 all other Metazoa, that they must be regarded as on a by- 

 road of evolution. This has been emphasised by Professor 



A B 



FIG. 60. A Young Dicvema. 

 After Whitman. B. 'Female 

 Orthonectid. (Rhopalura 



Gia rdii ). After Julin. 



e., Ectoderm ; en., inner endoderm cell 

 with nucleus (); and embryo (on.). 

 Note the segmentation and the 

 fibrillation supposed to be muscular. 



FIG. 61. Salinella. 

 After Frenzel. 



1. Longitudinal section 



a., anterior ; /., pos- 

 terior. 



2. Transverse section. 



Ray Lankester in the term "Parazoa"; he speaks of them 

 as a sterile stock. 



Their origin is wrapped in obscurity ; it may be that they 

 are the non-progressive descendants of primitive gastrula- 

 like ancestors with a sluggish constitution. 



