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BULLETIN OF THE BUREAU OF FISHERIES 
to the stimuli to which it is normally subjected. These observations can not be 
made sucessfully in the field. 
Geotropism is characteristic of many different animals. Although the theories 
devised to explain this response are many and varied (see Cole, 1925-26; Crozier, 1928 
for complete bibliographies on the subject), there are only two hypotheses that seem to 
be acceptable: (1) A theory which proposes that the gravity responses depend on the 
otolith-apparatus (Lyon, 1905; Baunacke, 1913; Kanda, 1916, 1916b), and (2) a 
theory which suggests that geotropic orientation may depend on the stimulation of 
proprioreceptors in the symmetrical parietal musculature (Cole, 1917, 1925-26; 
Arey and Crozier, 1919; Crozier and Federighi, 1925; Crozier, 1928). During the 
spring, summer, and fall — that is, when the temperature rises above 10° C. and the 
animals creep about actively — Urosalpinx cinerea exhibits a very pronounced negative 
geotropism. Such a reaction is important in that it is successful in keeping the egg 
capsules from being laid on the bottom where they would be covered with silt and the 
embryos killed. 
That this is a geotropic response is shown by the following observations. It per- 
sists in the dark room and when the eyes are removed; and is not dependent on oxygen 
content because experiments have shown that animals in areated sea water, where 
presumably the water is saturated as to oxygen, will give the geotropic response. If 
an animal is allowed to adhere to a glass plate, the plate raised vertically, and then 
turned as a wheel on its hub, thus changing the orientation of the animal, the snail 
will always turn so that the siphon points up and the shell apex down. The direction 
of body turning — that is, either clockwise or counterclockwise — depends on the side 
on which the apex is placed since in every case the apex moves down. 
The explanation for the absence of any negative geotropism during the winter 
months is not altogether clear. Two hypotheses may be suggested: (1) The low tem- 
perature may bring about a reversal in the response as in lower animals (Massart, 
1891 ; Sosnowski, 1899), or else (2) negative geotropism is dependent on the activity of 
the animal, an explanation that is probably the true one. This loss of geotropism is 
significant for any method of control which plans on trapping the drill by means of a 
dredge (Moore, 1897) and also for the pillar method which is described later. 
The rheo tropic response is found among many animals (Schulze, 1870; Yerworm, 
1899; Wheeler, 1899; Parker, 1903, 1904; Tullberg, 1903; Lyon, 1904; Dimon, 1905; 
Jordan, 1917, 1917a; Arey and Crozier, 1919, 1921), and it seems to be dependent 
on different sense organs in different animals. Bonnier (1896) believed that the 
rheotropic reaction of fishes was dependent on the lateral line organ, while Parker 
(1903, 1904) showed that in Fundulus the receptor for this response is not the lateral 
line organ but the skin. Tullberg (1903) believed the ear to be the organ directly 
concerned with the reactions of fishes to currents. According to Lyon (1904) “the 
primary cause of orientation in streams of some uniformity of motion is an optical 
reflex, a tendency on the part of the animals to follow the field of vision.” Jordan 
(1917, 1917a) found for Epinephelus striatus Bloch that the end organs concerned in 
rheotropism are located in the integument and that these organs are the organs of 
touch, which also serve as the essential organs of current stimulation. 
If Urosalpinx cinerea is placed in a water current it will orient itself so as to 
bring the siphon pointing upstream, thS shell apex downstream, and move against 
the current. The response is definite and immediate. The removal of eyes and 
tentacles does not interfere with the normal behavior of the drill, and experiments 
carried on in the dark room also gave similar results. Here evidently is a rheotropic 
