470 
.T. GRAY. 
* 
In 1908 Baltzer showed that in hybrid eggs of the cross 
S p h ae r e c h i n u s g r a n u 1 a r i s S x S t r o n g y 1 o c e n t r o t u s 
livid us ? there is an elimination of fifteen chromosomes in 
the first two segmentation divisions. The eliminated chromo- 
somes are found as double units lying at the equator of the 
spindle (c f. his text-figs, ii a and vii). This is a condition similar 
to that shown in fig. 69 of this paper. In the reverse cross 
Baltzer found no elimination ; the cross was difficult to obtain, 
and, although most of the mitoses were normal, a few showed 
marked abnormalities. Text-fig. iii of his paper shows an 
irregularity in the nucleus which is strikingly similar to figs. 
21-25 of G. Hertwig', except for external form. (See also fig. 
50 of this paper.) 
The elimination of chromosomes from hybrid eggs has also 
been described by Tennent (18 and 19 ). He has shown that 
in the cross Toxopneustes ^ x Hipponoe ? thereisacon- 
tinuous elimination of chromosomes up to the 16-cell stage; 
while in the reciprocal cross no elimination occurs. 
A comparison of the cytology of hybrid eggs with that of 
eggs rendered pathological before or after fertilisation shows 
a. remai’kable similarity between the two. 
Kupelwieser (8) showed that when eggs of Echinus 
microtuberculatus are fertilised by the sperm of Mytilus 
gallopro viiicial i s the male chromatin remains inactive, and 
does not fuse with the female pronucleus. This is exactly 
similar to what happens if such eggs are treated with patho- 
logical sperm of the same species (Teichmann), or when eggs 
of Parechinus miliaris are fertilised by sperm rendered 
abnormal by strong radio-active treatment (G. Hertwig) ; 
compare Kupelwieser fig. 19, and G. Hertwig fig. 6. 
The characteristics of Baltzer’s hybrid eggs are likewise 
an elimination of chromosomes from the nucleus, and in 
exceptional cases abnormalities within the nuclear membranes 
(text-fig. X, Baltzer). 
As an appendix to his paper, Konopacki compares his 
results with those of Baltzer ; he is of the opinion, howevei’, 
that although the structures observed in the two cases are 
