450 SUMMARY OF CURRENT RESEARCHES RELATING TO 



have been absorbed from time to time, but these have been almost 

 entirely bred out. The reds may be of several shades, but there are 

 not sufficient data to separate them. (2) Black is the dominant of red. 

 (3) Black produces dun hybrids— registered " dun," " dark dun," etc., 

 when mated with light dun. (4) Donn or blackish-brown produces 

 brindle hybrids when mated with black, red, and light dun. (5) Red 

 produces yellow hybrids when mated with light dun." 



b. Histolog-y. 



Thymus of Teleosteans.*— J. Aug. Hammar gives an account of 

 the fully developed thymus in a large number of Teleosteans. He 

 emphasizes the epithelial origin and nature of the thymus reticulum. 

 The organ is an integral part of the epithelium of the branchial cavity. 

 He does not find evidence of the autochthonous origin of the thymus 

 lymphocytes. There is a migration of lymphocytes from outside during 

 the period of differentiation. Myoid cells sometimes appear in the 

 placode-like thymus before there is any appearance of vessels or con- 

 nective tissue ; these are not inclusions from without ; they are 

 autochthonous. As in higher animals, there is an age-involution of the 

 thymus in Teleosteans ; the involution is probably associated with re- 

 productive maturity. Starving brings about accidental involution of the 

 thymus. 



Structure of Red Blood Corpuscles.t— A. Lelievre and E. Retterer 

 describe those of frog, larval salamander, larval Alytes, and embryo 

 guinea-pigs and rabbits. From the surface of the nucleus there are 

 radiating trabecule passing to the periphery. Still more delicate trans- 

 verse threads unite these and form a reticulum. The meshes are closer 

 towards the periphery. The early red blood corpuscles of Mammals are 

 like those of other Vertebrates. 



Shape of Mammalian Red Blood Corpuscles.}— H. E. Jordan 

 believes that the biconcave disk is the normal shape, and that all other 

 shapes are simply variations or modifications of this. It is certainly 

 very much easier to conceive of a biconcave flexible disk changing into 

 a cup than the latter changing into such a regular disk as is characteristic 

 of rouleaux. As a result of his examination of the omentum of the 

 cat under ether, hanging-drop preparations of human blood, and sections 

 of tissue from several domestic Mammals, he confirms the conclusion of 

 Weidenreich and Lewis that mammalian blood contains " bell-shaped " 

 or " cup-shaped " red corpuscles ; but he is compelled to take issue with 

 them in their opinion, that this represents the normal form, and that 

 the biconcave disks are artefacts. His observations lead him to interpret 

 all variations in normal blood from biconcave disk-shapes as the result 

 of the operation of extrinsic physical factors, necessitating adjustment 

 to narrow confines, or obstacles, or currents, or as the result of contact 

 with viscid bodies (other corpuscles), and of unequal contraction. 



* Arch. Mikr. Anat., lxxiii. (1908) pp. 1-68 (3 pis. and 10 figs.). 

 t G.R. Soc. Biol. Paris, lxvi. (1909) pp. 17-18. 

 % Anat. Anzeig, xxxiv. (1909) pp. 406-12. 



