40 
BUI.LETIN OE THE BUREAU OF FISHERIES. 
Next two packets of white cheesecloth of a similar size and appearance were made 
up. One of these contained a stone, the other a crab. This experiment was repeated 
four times on different days. The packet containing the crab was found in each case in 
from 3 to 5 minutes, while the one with the stone was never molested. The two packets 
were placed from lo inches to 3 feet apart. Once or twice a dogfish which had eaten a 
crab would return and, circling about the spot where the crab had been found, would 
approach the packet containing the stone in an inquiring sort of way but at no time 
touched it. The packet containing the crab was always shaken and bitten until the 
food could be removed and eaten. 
A crab was killed and a piece of white cheesecloth saturated in its juices. This was 
then attached to a small stone. In two experiments the presence of a food substance 
was noted in two minutes. The stimulus was located by the usual circling method and 
the stone, with its saturated cloth, seized again and again and shaken violently. After 
a half hour the fish took no further notice of it, probably because of a complete diffusion 
of the juices in the water. 
In all the above experiments a number of different sets of dogfish were used. There 
were usually from 6 to 8 fish in the pool at a time. Normally only one or two experiments 
a day were performed, in order that there be no interference between them. 
These observations show beyond doubt that the dogfish obtains its food through the 
use of a chemical sense. Experiments were now undertaken to find out what part the 
olfactory apparatus plays in these reactions. 
Four dogfish which had eaten readily when in the normal condition were removed 
from the pool and their nostrils stuffed with cotton wool ; in two of the cases the cotton 
was covered with vaseline. When returned to the pool such fish rush about violently 
for a few minutes, as do all dogfish which have been out of water. They soon, however, 
quiet down and swim about the pool as do the normal fish. Twenty-four hours later 
three crabs were placed, an hour apart, in the pool, which now contained, in addition, 
four normal fish. All were found, in the usual manner and length of time, by the fish 
without cotton in the nostrils. At no time did any of the individuals with the nostrils 
filled show the slightest interest in the crabs, although such often swam within a few 
inches of the food. Moreover, these fish made no attempt to follow those which had 
secured one of the crabs, although the food was occasionally dropped. It was often 
observed that two dogfish, one normal and the other with the nostrils filled, would be 
swimming along the wall side by side when they approached the vicinity of the crab; 
the normal fish would then make the usual sudden turn to search for food, while the 
individual with the cotton continued on its way with no change in the lazy swimming 
movement. As it was noted that vaseline or a close packing of the nostrils with cotton 
caused suppuration in time, this experiment was repeated three times with the cotton 
loosely packed. Results similar to the above were secured in all cases. Two tests were 
made, also, in which there were no normal fish in the pool. In these cases the crabs 
were left untouched for 24 hours, although the dogfish on the opposite side of the screen 
became much excited. 
