EARLY STAGES OF SEGMENTATION OF ECHINUS HYBRIDS. 501 
thereforej be concluded with complete confidence that our 
results obtained from these hybrids are entirely typical. 
Esculentus ? x Miliar is (?. 
The eggs of this cross preserved in 1912 were mostly in the 
2-cell stage, but a considerable number also show stages in 
the first division. Almost all are fertilised and in general are 
developing quite normally. No elimination of chromosomes 
nor formation of vesicles was observed, and the mitotic figures 
are in most cases as regular as in the eggs of the pure species. 
The spindles are less noticeably narrow than those des- 
cribed in the cross ac utu s ? X m ili a r is (J, but are probably 
narrower than in pure esculentus eggs or in esculentus 
? X acutus (J; divided poles are not found. Counts of 
chromosomes leave little doubt that the number is 36. Seven- 
teen counts of anaphase groups, in 11 eggs, gave 36 in nine 
cases (7 eggs), including nearly all the most satisfactory 
figures; 37 in two cases in wliich a pair, counted as two, 
are probably really one V-shaped chromosome; and in six 
counts either 34 or 35. Some of the cases in which 36 
are seen are so clear that there can be little doubt that it 
is the true number (fig. 28). If our estimate of 34 for 
miliar is and 38 for esculentus be correct, 36 is the 
number to be expected. One V-shaped chromosome is com- 
monly visible; there are two in esculentus, and none (pro- 
bably) in miliaris. In a considerable number of the 
anaphase figures (about eight out of twenty examined on 
this point), no V could be found, and for a time we thought 
that this body might be comparable with the hook-shaped 
chromosome found by Baltzer in half the eggs of Strongylo- 
centrotus and the horse-shoe found in half those of 
Echinus microtuberculatus.^ Further study, however, 
has convinced us that in our material it is almost impossible 
to determine with certainty the presence or absence of this 
element; when seen sideways it is practically indistinguish- 
* ‘ Ai’ch. f. Zellforsch.,’ ii, 15*09, p. 549. 
