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SUMMARY OF CURRENT RESEARCHES RELATING TO 
abdominal cavity. There is no accurate correspondence between the 
degree of external and internal budding. Situs inversus viscerum 
remains a puzzle. J. A. T. 
Fecundity of Top-Minnow. — R. L. Barney and B. J. Anson, 
Anat. Record , 1921, 22, 317-35, 2 pis., 3 figs.) The American viviparous 
top-minnow, Gambusia affinis , is of much importance as a mosquito- 
destrover. A study of its reproduction is interesting. There is a tissue 
investing the ovary and a definite genital duct. The ova that appear 
subsequently as liberated young are all fertilized at once. As the 
fishes increase in size, their fecundity increases. It appears that 80 p.c. 
of the annual production of young occurs before there is any consider- 
able decline in the temperature of the water. But besides temperature 
there is an internal factor : the egg-production is influenced by the size 
and metabolic potentialities of the female for that season. J. A. T. 
Tunicata. 
Reactions to Light in Larvas Amaroucium. — S. 0. Mast ( Journ . 
Exper. Zool ., 34, 149-87, 10 figs.). The tadpole-like larvae have a 
single eye, seated laterally at the posterior end of the body near the base 
of the tail. It has a lens, a pigment cup, and optic nerve-endings. 
When the larvae emerge from the colony they are for a short time strongly 
photo-positive ; after a few moments they become photo-negative, and 
remain so until they become attached. They rotate rapidly and continu- 
ously on their longitudinal axis. If the light is rapidly reduced the 
resting specimens become active, and the active specimens change 
their direction, the positive ones turning towards the abocular and the 
negative ones towards the ocular side. Increase of illumination does 
not affect resting specimens ; but negative active specimens turn 
toward the abocular side. The reaction time is so short that if the 
hand is moved up and down in front of the microscope as rapidly as 
possible, alternately increasing and decreasing the luminous intensity, 
the tail in attached specimens swings from side to side in harmony with 
the movement of the hand. Gradual changes in illumination have no 
effect. The photic reactions probably depend on the illumination of the 
nerve-endings. Orientation is the result of one or more shock reactions 
caused by the alternate shading and illumination of the optic nerve- 
endings, owing to rotation on the longitudinal axis. After the tadpoles 
are oriented, the retina is continuously approximately equally illumined ; 
the shock reactions cease ; the tadpoles continue on the course established. 
In this organism orientation is in no way dependent upon a balanced 
effect of stimuli acting continuously on symmetrically located photo- 
receptors, as suggested by the Decandolle-Verworn theory of orientation 
accepted by Loeb and others. J. A. T. 
De-differentiation in Perophora. — Julian S. Huxley {Quart. 
Journ. Micr. Sci., 1921, 65, G43-97, 3 pis., 1 fig.). The social Ascidian 
Peropliora viridis may de-differentiate in either of two distinct ways, or 
by a mixed method : (A) by reduction to a spheroidal mass, as in 
