132 



LEECHES 



this Stage there is a large fluid-filled space within the covering of 

 ectodermal cells and the gut rudiment is small, occupying only 

 a fraction of the available space. However, it soon acquires an 

 opening to the exterior and begins to absorb nutriment from the 

 fluid in the cocoon. This enables the endodermal cells to grow 

 and divide until the gut occupies the greater part of the embryo 

 (Fig. 84). 



Mesobia 



Mesode 



Germ 



Fig. 84. Sagittal section of advanced embryo of Piscicola, 



showing the germinal bands and developing gut. From 



Dav^^ydoff, 1959, after Schmidt. 



While this has been going on the germinal bands have become 

 well developed and the embryo possesses essentially the same 

 structures as are present in the embryos of other groups after 

 gastrulation : a gut with a stomodaeum but not a proctodaeum ; a 

 pair of germinal bands destined to give rise to the nervous system. 



