The origin and histogenesis of the thymus in Raja batis. 409 



subject for new research, there seemed to be none more likely. At 

 such phases the spleen had no existence, there was no rectal gland 

 or coecum, and, in fact, lymphoid structures of any and every sort 

 were entirely wanting. 



For reasons connected with the illustration by a skilled artist of 

 the projected memoir upon Scyllium this form was then laid aside, 

 although later on its embryos were more than once studied. The 

 present writing will deal almost exclusively with Baja hatis, not 

 because the facts made out in Scyllium are at all opposed to those 

 to be detailed concerning Raja, but for the reason, that the embryos 

 of the latter furnish pictures of a more beautiful description, easier 

 to understand, and much better suited for demonstration, than such 

 of the former. In Raja, and, so far as I have studied the matter, 

 this holds for the species R. radiata and R. clavaia equally with 

 R. batis, the preparations are so clear as to carry conviction. 



Table of Embryos, their Sizes preserved, and the 

 Figures from them. 



