53 HOWELL. [Vol. IV. 



(15) and by Schafer (16). Both of these observers have found 

 in the fcetus, or in the new-born mammal (rat), large connective 

 tissue cells, within which red corpuscles are produced endoge- 

 nously. The cells become elongated, and connect with one 

 another to form capillary blood-vessels. The newly formed 

 corpuscles are never nucleated, and in this respect differ from 

 the corpuscles produced endogenously in the germ layers of the 

 embryo according to Balfour and others. In his recent book, 

 Hayem confirms the work of Ranvier, and states in addition 

 that blood plates as well as red corpuscles can be seen in the 

 vaso-formative cells. The haematopoietic value of these cells 

 cannot be very great, as they have not been found at any other 

 period in the animal's life, except at birth or shortly afterward. 

 It seems to me that more extended observations are needed 

 before we can accept such a peculiar method of production as 

 one of the normal means by which new red corpuscles are 

 formed. Most of the recent work has shown that the red 

 corpuscles pass through a nucleated stage, and are not formed 

 endogenously within larger cells, so that the isolated observa- 

 tions even of such distinguished histologists cannot be weighed 

 against the combined work of so many other investigators. 

 Possibly the appearances upon which the theory is based may 

 be capable of another explanation. 



TJie White Corpuscles and Blood Plates during Embryonic Life. 



I have little that is new to add to our knowledge of these 

 two elements of the blood during embryonic life ; but the little 

 I have is worthy, perhaps, of being placed upon record, espe- 

 cially as it is a subject which seems to have attracted very 

 little attention and about which our information is deficient. 

 In the youngest embryo which I examined (cat, 2.5 cms. long), 

 no ordinary white corpuscles could be found, though the blood 

 was thickly crowded, of course, with nucleated and non-nucle- 

 ated red corpuscles. Occasionally a colorless corpuscle was 

 found ; but these differed so much from the usual white cor- 

 puscle of the circulating blood, from both the uninucleated 

 and multinucleated form, that it seemed probable that they did 

 not belong to the class of leucocytes, but were embryonic cells 

 which had got into the blood accidentally, either in opening the 



