218 H. D. Senior. 



this is probably a fact of great importance. The blood anlage of 

 shad (Type 1) arises as a cord of cells in the tail, which forms a 

 direct continuation backwards of the, then, partially developed 

 caudal aorta and caudal vein ; part of the blood anlage of Opsanus 

 tau (Type 2) also arises in a similar manner (the remainder arising 

 in the cardinal veins). It is possible that the tail is the site of blood 

 formation common to all teleosts, and that the cardinal vein blood 

 anlage occurs as a further source of corpuscles in the forms which 

 acquire numerous corpuscles at a comparatively early stage of devel- 

 opment. Without assuming this actually to be the case, I would 

 venture to suggest that, in connection with the origin of the blood 

 corpuscles, the tail deserves thorough examination in all teleosts, 

 whether or not, in the species under examination, corpuscles are 

 found to arise in the cardinal veins. Reference to investigations 

 setting forth the surface of the yolk as the source of blood corpuscles 

 has been purposely omitted. 



It has been my experience that the yolk in eggs of Type 1 is in 

 excellent condition for cutting after it has been fixed in formalin; 

 whereas formalin-fixation produces in eggs of Type 2 a yolk difficult 

 to cut and sometimes of almost stony hardness. This is not due 

 merely to difference in size, but seems to point to a difference in 

 chemical composition between the yolks of the two types of egg. 



It is well known that the differences in structure, and in the 

 general processes of development which occur among teleostean em- 

 bryos of different species bear little or no relation to the structure 

 and affinities of the corresponding adults; since, therefore, the type 

 of embryo cannot be inferred from the systematic position of the 

 adult, it would seem advantageous to classify the embryos them- 

 selves according to their own structural peculiarities. 



The division of embryonic teleosts into the morphological types 

 indicated above appears to be warranted by the present state of our 

 knowledge and, since it is applicable alike to pelagic, demersal, and 

 viviparous eggs it may prove of some service as a starting point for 

 classification. The demand for some such division into types is, 

 I think, indicated by the not infrequent use in the literature of 

 the terms pelagic and demersal in a morphological connection. The 



