44 Papers from the Department of Marine Biology. 



The main criticism of the above statement which I should like to 

 make is that Semper is mistaken in supposing that the crab moves 

 about so little in the cavity that one or two small fissures or apertures 

 alone suffice for the respiratory current. In my experience, in Pocil- 

 lopora the cavity is large enough for the crab to move about a good deal 

 in one plane and by observing the inhabitant of a nearly closed gall I 

 could actually follow such movements. I have never seen such scars 

 as Semper describes as due to the "continual scratching in one spot," 

 nor did Caiman. In saying that "as in all the crabs of this group" 

 (whichever group is meant) the respiratory current enters the branchial 

 cavity anteriorly (close to the mouth) and passes out posteriorly, the 

 case is exactly the reverse. Why it should be stated that both the 

 exhalant and inhalant streams should always flow in one and the same 

 direction I can not understand. As stated above, experiments with 

 carmine particles show that the exhalant current flows upwards and 

 outwards and the inhalant current laterally. Finally, in no galls that I 

 have seen are the apertures reduced to two. In Pocillopora there is 

 nearly always a considerable number (up to 10), of equal size and pre- 

 sumably importance, situated along a line which encircles the gall but 

 which is interrupted by the stalk. Only in a few old galls where inter- 

 nal growth has restricted the space do some of the apertures close up. 



GALL FORMATION IN STYLOPHORA AND SIDEROPORA. 



A species of Stylophora (S. raristella Dep. var wilsoni J. S. Gard.) in 

 the Cambridge Museum shows very well the formation of galls in 

 branching corals where the branches are more massive than in Pocillo- 

 pora and Seriatopora. The gall is produced apically, the branches 

 broadening out as in Pocillopora; but when fully formed the gall is 

 hardly distinct from the branch which bears it, its breadth and width 

 being little greater. The completed gall differs, moreover, from that of 

 Pocillopora in the fact that the approximated lips never show local 

 fusion, a narrow fissure of uniform width remaining between them 

 throughout the life of the gall crab. Here, then, the gall is truly 

 formed by the broadening of existing branches and not by the produc- 

 tion and fusion of new ones, and this is due to the larger scale of branch- 

 ing characteristic of the genus. This description applies also to the 

 genus Sideropora, as far as can be seen from the account and figures 

 given by Semper of galls in Sideropora palmata (p. 218, fig. 67) ; they 

 also occur in S. digitata. 



ACTION OF RESPIRATORY CURRENT ON INDIVIDUAL POLYPS. 



Speaking of the thecse which occur in the interior of the walls of the 

 gall, Semper says: 



"Not one of the cups is normal in structure; the depression, which in the 

 external polyps is very deep, is here no more than a shallow pit, and the 

 septa (or party walls) of the cup are very slightly developed. Hence it follows, 



