EARLY STAGES OP SEGMENTATION OF ECHINUS HYBRIDS. 495 
ill a normal way to the poles^ are seen to have vesicles 
attached to them. We conclude, therefore, that the tendency 
to vesicle-formation is diminished in the second division, and 
that nearly all the chromosomes which entered the nucleus of 
the 2-cell stage are able to divide and move to the poles in 
the normal way. Our material does not provide any examples 
of segmentation divisions later than the second in the cross 
acutus ? X esculent u s cJ , but we defer any discussion of 
the facts observed until the hybrids with E. miliaris have 
been described. 
E. ^IILIAPJS AND ITS CeOSSES WITH AcUTUS AND EsCULENTUS. 
The material obtained in 1911 included only one cross with 
E. miliaris, viz. acutus? x miliaris (?. Unfortunately 
the supply of pure miliaris eggs was small and not very 
good, so that we cannot give so full an account of it as of the 
other species. All the eggs showing mitotic spindles in pure 
miliaris were in the 4-cell stage or later, and owing to 
the small size and crowded state of the figures couuting was 
difficult. The chromosome number appears to be smaller 
than in the other species; many counts, especially of equa- 
torial plates, gave numbers ranging from 30 to 32 or 33, but 
ill two anaphase groups in one spindle, in which the chromo- 
somes were very clearly shown in face, 34 may be counted 
at each pole (fig. 21), and this number is confirmed by counts 
of the cross esculentus ? x miliaris (J (1912). The 
chromosomes are more nearly alike in size than in escu- 
lentus and acutus. 
Acutus ? X miliaris,^. 
In the eggs from the cross acutus ? x miliaris <S the 
spindles differ noticeably from those of the acutus and 
esculentus crosses (tigs. 22-25). The spheres with their 
radiations are very large and conspicuous, and only rarely 
show any division. The spindles are much narrower, with the 
