Hapalocarcinus, the Gall-forming Crab, etc. 43 
in the fully formed gall. But as I have indicated above, in Pocillopora, 
too, there is really an increased branching masked by immediate 
fusion of the branches, so that the process of gall formation is not 
essentially different in the two genera. 
It is rather difficult to follow the account of gall formation in Seria- 
topora given by Semper in ‘Animal Life.’’ This book represents a 
course of lectures given at the Lowell Institute in Boston in 1877 and 
I am not able to say whether a German edition of the book was ever 
published. The English work has, however, suffered very badly at the 
hands of the translator and it is sometimes difficult to determine what 
Semper intended to say. Take for instance the following sentence: “A 
diseased excrescence is first produced by the crab establishing itself 
between two branches, and the twig thus originating takes various 
forms according to the character of the species of coral.’’ What seems 
to be meant is that when the young crab establishes itself between two 
branches it modifies and stimulates the growth of each of them and the 
modified branches (twigs) take on various forms according to the species 
of coral which is in question. This is of course perfectly true and cor- 
responds to what I have said in the preceding accounts. The idea that 
the growth brought about by Hapalocarcinus is pathological is given 
in the application of the ungraceful term of ‘‘diseased excrescences”’ 
to it. This is entirely unwarranted, since similar modifications affect- 
ing the whole colony take place under the influence of wave action. 
There is, moreover, no reason for calling the crab a parasite, since it 
does not live upon the tissues of the coral; but even Calman falls into 
this error. 
Semper, after describing the process by which an open is converted 
into a closed gall, makes the following remarks: 
‘The creature requires a constant and rapid renewal of the water in the 
gall in which it lives, for the purpose of respiration; at first the water finds a 
free passage on all sides, but when the two twigs have bent over towards each 
other, the space through which it can find entrance and exit must grow nar- 
rower and narrower. Moreover, from the structure exhibited by galls broken 
off from the coral, it may be concluded with certainty that the crab moves 
about very little in the cavity, for otherwise we should not find the very 
distinct scars which are evidently produced by continual scratching in one spot. 
Since, in all the crabs of this group, the current of water for breathing enters 
the body close to the mouth, and passes out again at the hinder margin of 
the branchial cavity, the stream passing through the gall must always flow 
in one and the same direction. The results are easily recognisable in the half 
or wholly closed gall. The two excrescences on the coral grow together 
quickest in those spots which are least exposed to the current through the gall; 
there also they first come into contact, till at length only two fissures, more or 
less wide, are left, which plainly show, by their position opposite to each other, 
that it is through them that the current for respiration passes; one fissure 
serves for the influx, the other for the exit, of the water. These two slits 
remain open so long as the crab is alive; no living crab is ever found in a closed 
gall, and they are for the most part perfectly empty.” 
