464 Simon Henry Gage 



less, often many more. If the head is exposed and there are 

 any particles in the water a constant stream is seen to flow into 

 tlie mouth. Only when the respirations are very slow is the 

 stream into the mouth intermittent. 



As the burrow is ordinaril}- open, as shown in PI. VIII, Fig. 

 49, some particles of corn starch dropped into it diffuse in the 

 water and one can then see the direction of the stream from 

 the particles of starch. Starch is the most satisfactory sub- 

 stance used with the larval lampreys as they are not irritated 

 by it. In fact it is taken into the alimentary canal. In case 

 the water contains minute filaments these will often be drawn 

 by the stream to the mouih, but the sieve or net work formed 

 by the oral tentacles catches them and prevents their entrance 

 into the respiratory chamber. Whenever the oral sieve be- 

 comes at all clogged by adhering particles, the current is re- 

 versed and the offending debris washed off most energeticall}'. 

 If attention is directed to the branchiopores or gill openings, 

 it is seen that, with every constriction, streams of water shoot 

 out obliquely caudad. The valves over the branchiopores 

 (PL VIII, Fig. 52, vl.') project outward, but as soon as the 

 branchial apparatus expands for inspiration the valve closes 

 the branchiopore so that water does not enter it, and thus all 

 the water entering the gill cavities must enter through the 

 mouth. It is seen also that while the stream into the mouth is 

 practically continuous, its exit through the branchiopores is 

 intermittent. 



If a larva is placed in a dish of water it swims around 

 somewhat aimlessly but rapidly for a time, but finallj' rests on 

 its side. The side on which it lies seems to be a matter of 

 indifference, and is therefore sometimes the right and some- 

 times the left. If the water in the vessel is not too deep, the 

 current made by the jets of water from the branchiopores is 

 easily demonstrated by putting bits of wood or cork on the 

 water over the gill-openings. They follow the current almost 

 directly caudad along the whole length of the larva. If the 

 position of the larva is noted, and then it is observed again 

 after 15 or 20 minutes it is seen that it has moved cephalad or 

 forward due to the recoil or reaction of the jets of water forced 



