EARLY STAGES OF SEGMENTATION OF EC'HINFS HYRIMDS. 485 
probable that some chromosomes are missing or concealed. 
The chromosome groups of the two species are very much 
alike ; we have spent a considerable time in trying to discover 
points of difference Avhich might be used in the study of 
hybrid eggs, but have failed to find any that are trustworth}’. 
The chromosomes differ considerably in size and shape; in 
early anaphase figures seen in side view the following points 
are usually recognisable. (Fig. 3) : Two chromosomes are 
noticeably longer than all the rest, and commonly complete 
their division slightly later than the remainder. Two are U- 
or V-shaped; if seen with the two limbs almost superposed 
they are recognisable by their apparently greater thickness. 
About four are loiiger than the remainder, though shorter 
than the two long ones mentioned above, and are not usually 
hooked at the ends; these, however, are not always dis- 
tinguishable from the somewhat shorter rod-shaped chiomo- 
somes. The remainder are about equally divided between 
bodies the length of which is several times as great as their 
width, and shorter rods which often appear as oval or round 
dots if seen slightly obliquely. The chromosomes of both the 
last classes are frequently hooked at the end towards the 
pole ; sometimes this is so pronounced as to cause them to 
resemble the V-.shaped bodies mentioned above. Since the 
various classes described grade into one another almost 
imperceptibly, and are so similar in the two species, we have 
not been able to distinguish paternal and maternal chromo- 
somes in the hybrid eggs in the crosses between acutus and 
esculentus. 
The eggs of the pure species differ from those of the hybrids 
in the greater uniformity of the rate of development. In 
any batch of eggs of acutus or esculentus the majority 
are in stages of development not very far removed from one 
another, though there is not absolute uniformity. In the 
hybrid eggs, however, there is great diversity, and this 
appears to be the case to about the same extent Avhichever 
way the cross is made. In batches of which some eggs have 
reached the four-cell stage, others will show prophases of the 
