272 BULLETIN OF THE 



scales. The form ami development of these latter structures impart a peculiar 

 outline to the Athonjbia. The float (a) is large, pear-shaped, and sometimes 

 it protrudes above the circlet of covering-scales, as in the figures of A. mdo, Q. 

 & G., but generally it is drawn below the upper edges of the bracts so that it 

 can only be seen by looking through the body of the scale. When seen from 

 above, the float has a cherry or claret-red color on tlie periphery surrounding 

 a dark brown middle. In the centre there appears an opening giving a free 

 communication between the air-bladder (a a) and the surrounding water. 



The air-bladder (a a), which hangs within the float, is an elongated sac sus- 

 pended from the imier walls of the upper pole of the float. It resembles 

 closely the air-bladder of Agabna, and is destitute of those finger-like processes 

 which characterize the same structure in lihizojyhysa. No communication was 

 observed between the cavity of the float and that of the axis. Swimming-bells 

 are wanting in Athoryhia. 



The covering-scales arise from all sides of the short axis below the float, and 

 in their method of attachment to the rudimentary stem are not unlike the 

 petals of a flower. When seen from the side, they give the whole animal a 

 rhomboidal shape. The covering-scales (PI. VI. fig. 14) are curved and spatu- 

 late, with the convex surface turned outward. At its origin the bract is narrow, 

 but gradually as it i-ecedes from that point it widens, and its bounding edges 

 are indented with a pair of teeth, one on each side about two thirds the distance 

 from the attachment to the distal rim of the scale. The outer, convex surface 

 of the covering-scale is slightly rounded laterally, and is crossed by four rows 

 of lasso-cells {I) arranged in longitudinal lines.* When the scale is seen from 

 one side it appears serrated along these four lines. The scale of the Athoryhia 

 stage in the young Agalma has a somewhat similar serrated appearance. Along 

 the medial line of the bract, on its inner concave surface, there runs a longi- 

 tudinal vessel which communicates with the stem cavity and ends blindly at 

 the most distal extremity of the scale. 



From their position of attachment, as commonly carried, the scales at first 

 extend outward almost at right angles to the axis of the float, and the natural 

 curvature which they have imparts the somewhat spherical outline to the 

 animal. These covering-scales can be made to extend themselves or draw 

 together, receding from or approaching the line passing through their attach- 

 ment and the apical portion of the float. This expanding and contracting power 

 of these bodies is limited to the extremities, which are moved apparently by 

 muscles in the base of the scale and its peduncle. The motion of the scale may 



* Huxley (op. at., p. 86) says the outer surface of the covering-scale in his 

 species of AOioryhia is crossed hy six rows of small thread-cells. KoUiker describes 

 the bract of A. rosacea as crossed hy Jive or six white ribs, formed of small lasso-cells 

 which sometimes traverse the whole length of this structure and sometimes do not. 

 The same may be said of the lines of lasso-cells in the bract of A. rosacea, with the 

 exception that in no specimen were there more than four ribs of these bodies. Tlie 

 specimens which were taken may have been immature, and other specimens may he 

 found with six lines of these cells, as in A. rosacea. 



