HYDROIDA. 



39 



divergent from the stem or the parent branch ; Ritchie says 

 " almost at right angles," but his photograph shows much 

 variation in this respect, from 1)0° to about 60°, while some of 

 the secondary branches have an angle of only about 45°. It is 

 to be noted that before an accurate notion can be obtained as to 

 the character of the branching in most species they must, if dry, 

 be immersed in water to make them resume their natural form. 

 According to Ritchie, the two series of branches, are in two 

 planes meeting at a wide angle. 



A. tasmanica is a good deal like A. crucialis in habit, my 

 specimens having comparatively slender stems about a foot high, 

 and bare about half way up. The branches have an angle of 

 about 50° or 55°. Both series are in one plane and all face in 

 the same direction. 



A. billardi is very similar to the last ; in my specimens the 

 hydrocladia and branches are confined to the top three inches, 

 the stems being about a foot in height. The branches are less 

 divergent, being at angles of about 45 c , otherwise the habit is 

 much the same. 



Of A. macrocarpa the best specimen is about three inches in 

 height and broken off both above and below. It bears on the 

 upper half two pairs of branches, and has the hydrocladia 

 extending flown to about the origin of the first pair. The stem 

 and branches, especially the former, are much stouter and more 

 rigid than any which I have seen on the hydrocladiate portions 

 of the other species. 



The branches, though subject to much irregularity, are mostly 

 in opposite pairs, and not in the same plane ; they diverge from 

 the sides of the stem at angles of about 55° or 60°, and are also, 

 at their origin, directed well forward, so as to take them out of 

 the plane of the stem; - they soon, however, take a characteristic 

 curve upward, becoming erect, and even in some cases incurved 

 in the distal portions (PI. i., figs. 1 and 2). The habit thus differs 

 from that of the two other species, in which the whole polypidom 

 is flat and the branches straight and comparatively slender. 

 Associated with the habit of A. macrocarpa, however, is a further 

 peculiarity, namely that the anterior aspect of the branches, from 

 which the hydrocladia spring, faces that of the stem or parent 

 branch, contrary to the condition in A. tasmanica, A. billardi, 

 and indeed in all species known to me in which the polypidom 

 occupies a single plane, where the stem and all the branches 

 normally face the same way, so that such species are easily seen, 

 even by the naked eye, to have a " back " and a " front " to the 

 polypidom as a whole. 



