BOTRYLLUS SCHLOSSERI (PALLAS). 



in a glass cylinder, the bottom of the container must of necessity 

 become the place of attachment of a large proportion of the 

 zooids present in it. The remainder which metamorphose else- 

 where get caught at the top of the water or near small bubbles 

 of air on the side of the cylinder by surface tension, and still 

 others, in sinking strike the sides of the container, and attach 

 before reaching the bottom. A second explanation for the oc- 

 currence of metamorphosis at the bottom of a container standing 

 in a vertical position, may be found in the fact that the larvae 

 are negative in their response to light at the close of the free- 

 swimming period. Two experiments will serve to illustrate. 

 Larvae just liberated from the parent colony were allowed to 

 metamorphose in a cylindrical graduate placed vertically, the 

 sides of which had been partially covered with black paper. 

 Three bands of black paper covered the areas between the 100 

 and 200 cc. marks, the 300 and 400 cc. marks, and an equal 

 area above the 500 cc. mark. Thus alternating bands of light 

 and shadow, having the same areas were produced. Of the 127 

 larvae which attached to the cylinder, 82 attached in the dark- 

 ened areas, five to the sides in the undarkened areas, and forty 

 on the bottom. At another time larvae just liberated from the 

 parent colony were introduced into a glass cylinder of 1000 cc. 

 capacity the sides and top of which were completely jacketed 

 with black paper. The cylinder was held in an oblique position 

 at an angle of less than 45 degrees, and a 75-watt nitrogen bulb 

 w r as so placed that rays of light parallel with the long axis of the 

 cylinder passed into the column of water thru the uncovered 

 bottom. When sufficient time for metamorphosis had passed, 

 the location of the metamorphosing zooids was noted. A very 

 large proportion were found at the upper end of the cylinder, 

 away from the source of light. These results indicate that the 

 larva is not positive in its response to gravity at the end of the 

 free-swimming period, but that its negative response to light is 

 effective in leading it to the darkest part of the container. The 

 lowest part of the container, and in its natural habitat, the lower 

 levels of water are in general the darkest regions to which the 

 larva can gain access. Hence the negative response to light per- 

 forms very much the same function as would a positive response 

 to gravity. 

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