614 
T. H. MORGAN 
are unequally distributed, and are carried over into the blasto- 
meres, redistribution being thereby prevented. 
The formation of the aster and its relation to the chromosomes. The 
experiments in which the sperm-nucleus was carried away from 
its aster and only later was brought into relation with the segmen- 
tation spindle show that the sperm aster develops independently 
of the nucleus. In other words the aster does not appear to be a 
manifestation in the cytoplasm caused by the vicinity of the nu- 
cleus, but to be an independent development. The case of cen- 
trifuged polyspermic eggs also illustrates the same point. The 
evidence from a study of normal fertilization has shown that the 
aster develops around some body brought in by the sperm, also 
the experimental evidence makes clear that the material, so 
brought in, acts as the future center for aster formation. The 
genetic continuity of the centrosome thus introduced can in many 
cases be demonstrated, and even when it cannot be, the evidence 
still makes probable the view that new centers form in connec- 
tion with the old. This problem of the continuity of the centro- 
some and aster is, however, one that has not lent itself to such 
diagrammatic treatment as in the case of the chromosomes. 
Several years ago when Boveri proposed the theory that the cen- 
trosome was a body introduced by the sperm as the essential 
feature of division, I showed that by treating eggs of several 
animals with salt solution, artificial asters appear. A study of 
their origin revealed that they were not derived from a single 
center — as might have been claimed since the egg itself had 
also a past connection with centrosomes — but appeared independ- 
ently at any points in the egg. Their exact method of formation 
I was able to make out for several kinds of eggs. These asters 
resembled in everj^ way the normal asters, including a small 
deeply staining center or centrosome. They waxed in size as the 
cleavage process approached and faded later. The}' attracted 
the chromosomes as do normal asters. Wilson demonstrated 
later that they divided, and produced a spindle between the 
separating centers. 
It is clear that while in normal cell division a continuit}^ of the 
centrosomes may exist, that insures the regular occurrence of 
