346 
Th. H. ilorgan 
cases, and in nine species of flies she found an A' Y paii’ of chromosoines. 
Such an extensive study will not seera superfluous when tlie reception 
of this important discovery in regard to sex is remembered, for tlie 
profound significance of the results were by no means generally ap- 
preciated, and it is not going too far to say that niany cytologists assumed 
a sceptical or even antagonistic attitude for several years towards the 
new discovery. 
Four papers dealing with the chromosoines in the life cycle of Aphids 
appeared in 1905, 1908, 1909 and 1910. The double number of pah’ed 
chroniosomes was found in the parthenogenetic cycle, and the reduced 
nnmber in the sexual eggs and sperm. The parthenogenetic eggs were 
shown to give off a single polar body, the sexual egg two polar bodies. 
i\Iiss Stevens denied at first the presence of an unpaired sex chroniosome 
in the spermatogenesis, Init later corrected this error. She failed to note, 
at first, that the male had fewer chromosoines than the feniale, biit later 
recognized this difference. In her work on other insects she described 
both an end-to-ehd union of chroniosomes, as well as a side-to-side pair- 
ing, but her work on the synaptic stages was far less complete and con- 
vincing than that on other parts of the gerni-cycle. At the time of her 
death she was engaged in studies directed inore especially to this difficiilt 
phase of gametogenesis. 
She discovered in the Muscidae that the honiologous chroniosomes lie 
side by side in each spermatogonial and oogonial division, as well as 
before synapsis. Even in soniatic division a siniilar pairing was found. 
In CeuÜiopliiliis one to three supernumerary chroniosomes were dis- 
covered, whose behavior in rest and in growth stages indicated, she 
thought, their probable relationship to the sex chroniosomes (1912). 
Previously, she has found that the presence of supernumerary chromo- 
sonies in Diahrotica led to a variable number (with fixed limits however) 
of chroniosomes in different individuals of the sanie species. 
In the regenerative processes in the hydroid Tubularia, Miss Stevens 
found that the old tissues beconie remodeled into the new without under- 
going any retrogressive changes, and a siniilar condition was found in 
Planarians. In Sagitta the true oviduct, previously overlooked, was 
described and its development, and that of the ovary also, were thoroughly 
stiidied. 
Sonie interesting facts in regard to the color of the parthenogenetic 
and sexual fornis of Aphids were recorded, but the study of the inheritance 
of these colors was not broiight to completion, although certain possi- 
bilities were indicated. 
