148 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the one hand, it is advantageous in fixing character and developing pre- 
potency ; on the other hand, there is a necessary lessening of the possible 
range of variability, and a risk of degeneration if a taint occur, or the 
obscure limits of stability be exceeded. 
(4) A number of experiments have been made likely to give telegony 
the best possible chance of declaring itself; and although Prof. Ewart 
abstains from dogmatic conclusions, and suggests a whole series of ex- 
periments which should be made, the verdict is clear that so far the 
case for telegony is non-proven. Though we have given the merest 
outline of the results, we have said enough to show that this interesting 
volume is a timely and important contribution to the study of heredity 
and kindred problems. 
Functions of the Thymus.* — Dr. J. Beard begins a very interesting 
paper on 11 the true function of the thymus,” by noting that there is 
hardly an organ in the body about whose function in the embryo and 
at later periods so little is really established. 
Since Kolliker discovered its mode of origin in mammals from the 
epithelium of a gill-pouch, and stated that the original epithelial cells 
give rise to lymph-cells or leucocytes, two positions have been held in 
regard to the thymus. Some, like Stieda and His, have maintained that 
the leucocytes so characteristic of the thymus have migrated thither 
from the exterior, possibly from the mesoblast. Others, like Kolliker 
himself, maintain that the original epithelial cells of the thymus give 
rise to lymph-cells or leucocytes. 
Dr. Beard has studied the question for many years in Raia batis , the 
smooth skate, but has only now reached conclusive results. At the 
period when leucocytes first appear, there is no spleen, nor rectal gland, 
nor lymphoid structures of any kind, but the primordia of the thymus 
are present, and it is from their epithelial cells that the first leucocytes 
are formed. When the thymus elements set to work in earnest to form 
leucocytes, i.e. in embryos of 28 mm. and upwards, these wandering 
cells, true to their “ hereditary instincts,” begin to emerge in crowds, 
causing larger or smaller “ breaks” on the contour of the thymus. 
It is Kolliker’s great service to have shown that leucocytes arise in 
the thymus from its original epithelial cells ; to Gulland’s researches 
we owe the result that the first leucocytes are found in the mesoblast in 
the neighbourhood of the thymus ; and Dr. Beard has now shown that 
the first leucocytes arise in the thymus from its epithelial cells, and that 
thus it is the parent source of the leucocytes of the body. 
Experimental Embryology.t — Prof. 0. Hertwig has made experi- 
ments on the influence of centrifugal force on the developing ova of the 
frog. When this is exerted in a certain degree (experimentally deter- 
mined) on the eggs of Rana esculenta, it produces a more marked separa- 
tion of the lighter and the heavier substances, in consequence of which 
the cleavage process is restricted to the “animal half ” of the ovum. 
In the course of segmentation the ovum assumes a character quite di- 
vergent from the normal, and in fact very closely approximating to 
the meroblastic type. An undivided yolk-containing portion occupies 
* Lancet, Jan. 21, 1899, 11 pp. 
f Arch. Mikr. Anat , liii. (1898) pp. 415-44 (2 pis.). 
