74 Bulletin Wisconsin Natural History Society. [Vol. 10, Nos. 1 & 2. 
Godlewski (’06), crossed Echinoid eggs with sperm of Crin- 
oids. Baltzer, in 1910, produced somewhat similar crosses. In 
1911, Godlewski succeeded in producing crosses between Echino- 
derm eggs (Sphcerechinus, Strongylocentrotus, etc.), with the 
sperm of the Annelid Chwt opt eras, and also with the sperm of the 
Mollusc Dentalium. He, for the first time, was also able to show, 
cytologically, that the sperm actually penetrated the egg. 
Kupelweiser (’06, ’09), crossed Echinoid eggs with Mytilus 
sperm, and Tennet (To), successfully crossed the eggs of Tox- 
opneustes with Holothuria sperm. 
In all of the above cases the yolk membrane was called forth, 
but unless the eggs were transferred to a hypertonic solution of 
sea water, cytolysis sets in, and the eggs disintegrate. When the 
change to the concentrated medium is made, however, develop¬ 
ment proceeds to the gastrula and even to the pluteus stages. 
Godlewski (Ti), showed conclusively that although the sperm 
of Chcetopterus actually enters the egg of the Echinoderm, it 
nevertheless plays no part in the development of the embryo, for 
it is thrown out very shortly after its entrance. Its action, prob¬ 
ably, is similar to that of the acidulated sea water, tending to call 
forth the yolk membrane. These so called crosses may thus be 
said to be mere cases of artificial parthenogenesis; the foreign 
sperm acting like chemicals, as stimuli toward development. 
This phase of experimental work is so young that one cannot 
speak with any certainty as to its probable fruitful disclosures 
within future years. The progress already made, however, makes 
one thing definitely certain, and that is that development is essen¬ 
tially a metabolic process, depending upon certain chemico- 
physical conditions of the female germ cell. 
D. parthenogenesis and sex. 
Nearly all investigators working on the problem of sex determ¬ 
ination, are of the opinion that the sex of zygote is fixed at a very 
early period, and that it is not dependent upon environmental 
factors acting on the developing embryo. It is true that external 
influences may modify the structure of the resulting individuals 
considerably, but there has been no proof brought forward to show 
that the sex of a developing egg can be modified by environmental 
conditions. All that the experiments on parthenogenetic forms, 
