76 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the collection of tlie Philadelphia Academy. Several new genera and 
species ai-e established, and [not a few changes in the nomenclature have 
been introduced. 
Nervous System of Shore-Crab.* — Herr A. Bethe has conducted an 
elaborate series of investigations on the anatomy and physiology of the 
central nervous system in Carcinus msenas. The paper does not readily 
lend itself to the purpose of a summary, but the following may serve to 
indicate its scope. The anatomy of the brain and thoracic mass is 
described in detail, a complete analysis of their elements being given. 
A full description is given of the habits, and movements of the living 
normal animal, including some interesting observations on food-taking, 
relation to light, and so on. The animals habitually avoid light, and 
seek corners where the body is partially concealed ; a strong light will 
cause them to leave these lurking-places ; but even blind animals seek 
places of concealment — a phenomenon described by the author as “ posi- 
tive kalyptrotropism.” The paper also includes an account of numerous 
physiological experiments on the crab. The otocysts or statocysts are 
regarded as organs having to do with the maintenance of equilibrium, the 
relation of the body to the horizontal plane. They are thus contrasted 
with the semicircular canals of Vertebrates which have to do with the 
perception of the degree and direction of a movement, especially of a 
rotatory movement. 
Development of Nervous System and Sex-Cells in Lernsea bran- 
chialis.f — Herr D. Pedaschenko finds the apical plate to be at first un- 
paired ; it becomes divided into two lateral portions, which probably 
pass into the frontal sense-organs. A continuation of the apical plate 
on the ventral surface forms the “ procerebrum ” ; the “ secondary brain ” 
(rudiment of eyes and optic ganglia) arises from paired dorsal thicken- 
ings. The two halves of the ventral cord arise independently. 
During the epibole four micromeres sink below the ectoderm and 
form the primary genital cells. 
There are two median dorsal organs, formed of high prismatic ecto- 
derm cells. In later stages these are insinuated beneath the ectoderm 
and absorbed by the yolk-cells. 
Vertical Distribution of Limnetic Crustacea.^ — Mr. E. A. Birge has 
studied this in Lake Mendota, Wisconsin, since July 1894. The factors 
are numerous and their action is complex. “ The quantity and kind of 
food in any stratum of the water constitute a prime factor in determining 
its crustacean population. The distribution is also modified by light, 
temperature, gravity, wind, and the chemical condition of the water. 
These forces act in different ways on different species, and also act 
differently on the individuals of the same species at different ages ; and 
in many cases have more effect than food on the vertical distribution of 
the Crustacea.” 
Annulata. 
Physiology of 01igochaetes.§— L. Cuenot has made investigations on 
the following points : — (1) Deserve substances. The typical reserve is 
* Arcli. Micr. Anat., 1. (1897) pp. 460-546, and 589-639 (7 pis.). 
t Trav. Soc. Nat. St. Petersbourg, xxvii. (1897) pp. 187-94. See Zool. Centralbl., 
av. (1897) p. 844. f Biol. Centralbl., xvii. (1897) pp. 371-4. 
§ Arch. Biol., xv. (1897) pp. 79-124 (2 pis.). 
