ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
605 
trances of the nerves into the retina acquire a more lateral superficial 
position, thus resulting in the more or less inverted form of the cup- 
eye. In front of the retina groups of hypodermis cells may form 
lens structures. Finally the more or less depressed eye-cup, and, 
in cases of fusion, the tripartite eye-complex, acquires a mesodermic 
sheath which is continued directly into the neurilemma of the nerves 
to the retina. 
Apodemes of Apus and Endophragmal System of Astacus.* — 
Mr. H. M. Bernard sets himself to show how Apus, with its powerful 
ventral longitudinal muscle-bands and its flexible skin, affords us a com- 
plete explanation of the endophragmal system of Astacus. In the latter 
the ventral muscle-bands, except those specialized for moving the tail, 
have almost entirely disappeared, and the deep folds of skin which the 
now vanished ventral muscles had called into existence, have become 
permanent calcified ridges, fastened together by sinewy connective tissue. 
Correlated Variations in Crangon vulgaris.| — Prof. W. F. R. 
Weldon has attempted to apply Mr. F. Galton’s method of finding a 
constant relation between the variations in size exhibited by one organ 
of an animal body and those occurring in other organs to the measure- 
ment of the correlation between four organs of the common shrimp. 
The organs measured were (1) the total carapace length, measured in a 
straight line ; (2) the length of that portion of the carapace which lies 
behind the single gastric spine ; (3) the length of the sixth abdominal 
tergum ; and (4) the length of the telson. Five races of shrimps have been 
studied, and of the examples one thousand were females from Plymouth. 
The author does not pretend that the results which he gives are 
sufficiently numerous or accurate to serve as a basis for generalization, 
but they do seem to suggest a very important conclusion. “ For, if the 
values of the constant have really the degree of constancy which has 
been attributed to them, then by expressing the deviation of every organ 
examined from its average in terms of the probable error of that organ, 
the deviation of any one of these organs from its average can be shown 
to have a definite ratio to the associated deviation of each of the others, 
which is constant for all the races examined.” As the organs examined 
and the samples of shrimps were, in the first instance, chosen by chance, 
any result which holds for all these organs through all these races may 
be reasonably expected to hold generally true of all organs through the 
whole species. 
Prof. Weldon hopes that, by expressing the deviation of every organ 
from its average in Mr. Galton’s system of units, a series of constants 
may be determined for any species of animal which will give a numerical 
measure of the average condition of any number of organs which is 
associated with a known condition of any one of them. “ A large series 
of such specific constants would give an altogether new kind of know- 
ledge of the physiological connection between the various organs of 
animals ; while a study of those relations which remain constant through 
large groups of species would give an idea, attainable at present in no 
other way, of the functional correlations between various organs which 
* Ann. sind Mag. Nat. Hist, x. (1892) pp. 67-74 (1 pi.). 
f Proc. Roy. Soe., li. (1892) pp. 2-21 (4 tigs.). 
