I07 



The specimens from locality I. were particularly interesting, 

 as three types were distinctly visible in them. The descrip- 

 tions of each of these are given in the accompanying table. No. 

 3 were obviously young forms leading to Nos. i and 2, and 

 showing plenty of intermediates. Nos. i and 2, however, re- 

 present two distinct modes, between which odd specimens 

 existed, showing intermediate conditions in each of the charac- 

 ters which serve to separate them. Only two specimens were 

 at all doubtful in their position, and in one of these, of which 

 one side had apparently been broken down and regenerated, 

 half the corallum belonged to type i, and half to type 2. On 

 each of 450 of these specimens, besides a number from other 

 dredgings, I made 1 1 measurements, in an attempt to compare 

 them together, and to find out with some precision the charac- 

 ters of the species. The results were exceedingly disappoint- 

 ing, partially no doubt owing to the peculiar conditions existing 

 between the coral and its commensal Aspidosiphon, but mainly 

 owing, I believe, to the variation of these forms being purely 

 vegetative in their measurable characters, the direct result of 

 environment, ana hence of quite a different nature to that usually 

 included under the term " variation." 



My first attempts were to correlate (i) the length by (2) 

 breadth of calicle, (3) breadth of base containing the Aspido- 

 siphon, (4) height of whole corallum, and (5) weight of the dried 

 corallum. Of these, i to 4 are dependent on the age, size, and 

 rate of growth of the two organisms, as well as on the size and 

 form of the original shell, on which the coral affixed itself, and 

 also on the growth of the Aspidosiphon. No. (i) by No. (5) at 

 fiist gave better results, but the weight of the corallum is largely 

 influenced by the size of the gastropod shell and the weight of 

 sand in the body, or in the tube of the individual Aspidosiphons, 

 a variation ranging through 1 5 per cent, of the total weight. A 

 real meristic variation was found in seven specimens, i'2 per 

 cent., in the number of cycles of septa. The number is so small 

 that they can only be chronicled with the remark that in this, 

 as in all its other specific characters, the form is extremely 

 highly specialised, and more or less definitely fixed. Yet it is 

 particularly interesting to note that four of these were in the 

 much less numerous specimens of the 2nd type. In many of 

 the specimens some septa of a fifth order were present. They 

 formed 2\ per cent, of type i, and over 50 per cent, of type 2, 

 while the per cent, in young forms was intermediate ; it was 

 noticeable that in only one case where 6 systems were present 

 were there less than 48 septa. 



