272 BULLETIN OF THE 



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

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

 it protrudes above the circlet of covering-scales, as in the figures of A. melo, 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 the 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 inner walls of the upper pole of the float. It resembles 

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

 which characterize the same structure in Ilhizophysa. No communication was 

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

 are wanting in Athorybia. 



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 recedes 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 (') arranged in longitudinal lines.* When the scale is seen from 

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

 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 tin- 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 pawing through theii attach- 

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

 of these bodies is limited to the extremitit ■>, which are moved apparently by 

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



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

 species of Ath/rrybia is crossed liy six rows of small thread-cells. Kolliker describee 

 the bract of A. rosacea as crossed by five or six wliite ribs, formed of small lasso-oaUa ' 

 which sometimes traverse the whole length of this Structure ami soiietime-. do not, 

 The same may be said of the lines of lasso-cells in the brad of .'• ItNfMM, with the 

 exception that in do specimen wen- there more than lour ribs of these bodies. Tho 



Sp i iineiis which were taken may have 1 n immature, and other >\>r> im< lis may be 



found with six Hues of these cells, M in A. rosacea. 



