50 



MARINE AND FISHERIES 



1-2 EDWARD VII., A. 1902 



found in higher animals. The intestine coils completely round the test, turns and then 

 winds back again to end finally in the anus which is situated on the pole of the shell 

 opposite the mouth. The anus is surrounded by a specially modified plate of the test. 

 One of these apical plates is very distinct as it is much larger than the others. This 

 plate is perforated and through its fine pores the water vascular system is brought into 

 communication with the outside. 



The food in the digestive tract is surrounded by a mucinous secretion but such 

 secretion is never copious. In the secretion are ferments which resemble those 

 found in the pancreatic juice of mammals in that they act in neutral or alkaline media 

 but not in acid onfes. There is a diastatic ferment present which, however, acts slowly 

 on raw starch. There is also a proteolytic ferment present and probably a steatolytic 

 one but the tests for the latter were not conclusive. The ferments present retain their 

 hydrolytic activity through a long range of temperatures being active from near the 

 freezing point to 55° C. 



In the investigation of the food the contents of the digestive tracts of more than 

 300 urchins were examined. Most of these were from the littoral fauna in the immedi- 

 ate neighbourhood of St. Andrews, N.B., but some were obtained from L'Etang Harbour 

 and others from Deer, Indian and Dochet Islands. Besides these collected in shallow 

 water others were obtained by the dredge from different parts at different depths of 

 Passamaquoddy Bay. In the case of the littoral ones the piocedure was to go at low 

 water, carefully note the surroundings of the urchins, break through the test and 

 examine the contents of their digestive tracts. Specimens were taken from each locality 

 and the contents of their alimentary canal submitted to microscopical examination. 

 Urchins were also kept in clean vessels and in this manner their excrements obtained. 

 Dredged specimens were examined in a similar manner. An idea of their surroundings 

 was obtained from the character of the remaining contents of the dredge. 



The food, judged by the substances in their digestive tracts, varies with the local 

 conditions under which the animals live. Such conditions were carefully studied in the 

 case of the littoral urchins which are the ones the fishermen accuse of destroying the 

 seaweed. It was found that the entire character of the food might change within a 

 very short distance. In all cases where the urchins lived in close proximity to the large 

 fucoid or laminarian seaweeds, there was practically nothing but pieces of such seaweed 

 in their digestive tracts. The seaweed had been bitten in pieces a millimetre or two 

 long, and had been changed from the ordinary brown to a green colour owing to the 

 dissolution of its brown colouring matter. Urchins in these localities were frequently 

 found with pieces of seaweed in their mouths. In cases where the urchins lived at a 

 distance from the large seaweeds or where these were scarce, the digestive tracts con- 

 tained little globular masses of sand. On breaking one of these masses and examining 

 it under the microscope, the remains of the great variety of minute organisms which are 

 common on the bottom, or which may be f craped from seemingly bare rocks are observed 

 among the sand grains. The great bulk of these remains are those of microscopic plants 

 belonging chiefly to the Diatomacese but other minute Algae are also common. The 

 animals found in these masses are chiefly Radiolaria and other Protozoa, but occasionally 

 other minute animals, including larvse, are noticed. In a few cases carrion was observed 

 in the alimentary canal. Dead animals placed in the water are soon covered with urchins 

 which rapidly devour them. In lobster traps it is common to find considerable numbers 

 of urchins which are attracted, no doubt, by the dead animal matter used as bait. Al- 

 though carrion is soon found and devoured by the urchins it cannot be considered one 

 of their ordinary foods because its supply is erratic and uncertain. 



An examination of the excrements of the animal confirmed what was observed in 

 the intestinal canal. When the urchins were obtained near seaweed, the excrements 

 were small pieces of seaweed which did not seem greatly altered by their passage 

 through the intestinal canal, except in their colour. When the urchins came from 

 localities remote from seaweed, the excrements were the small globular masses such as 

 are observed in the alimentary tract. In tide pools where sea-urchins are abundant, 

 the bottom is frequently covered with a layer of the castings of these animals. 



The sea-urchin has thus two principal foods which we may call seaweed and surface 

 sand. The seaweed is cut into little pieces, whilst the sand with all the minute organisms 



