68 N. AnnaNDALE: The Fauna of Brackish Ponds. [VOL. I, 



fine thread were drawn tightly round it at one point (see plate iv, 

 figs. 3,4). Although any one of the strands can contract in this way 

 without affecting the others, I have observed under the microscope 

 that they very frequently contract rhythmically and in regular suc- 

 cession from below upwards. What happens is this : The pore in 

 the centre of the basal disk is opened and water is drawn into the 

 lumen of the disk, which becomes bulbular, the circular muscle 

 strands at the base of the column being strongl}^ contracted above it. 

 Then the pore is closed, the lowest muscle strand relaxes and the 

 second one above it contracts. Then the second strand relaxes and 

 the first contracts again, and, as the process is continued up the 

 column, the water is gradually driven up towards the mouth, just 

 as though it were being squeezed upwards in an indiarubber bag by 

 drawing tight and loosening in regular succession a series of elastic 

 rings. I have Httle doubt that it is by such means that the Actinian 

 is able to rise to the surface again after it has sunk into the mud ; 

 but I have only been able to observe such movements in the case 

 of young individuals which had not yet begun to burrow. In their 

 case the movements assisted them in making their way through a 

 tangled mass of alga filaments. The foot of adult individuals of 

 this variety is probably used for burrowing, aided by contractions 

 both of the circular and the retractor muscles ; but owing to the 

 difficulty experienced in keeping such individuals in a healthy condi- 

 tion after they have been removed from their natural habitat, I 

 have no direct observations to offer on this point. When large in- 

 dividuals are removed from the mud, the contractions of the column 

 which take place are very marked, but entirely lack co-ordination. 



Food. — 



Judging from dissected specimens, the food of the pond race 

 consists very largely of minute univalve Molluscs , the shells of which 

 are ejected after the animal has been absorbed, and of small fish such 

 as Haplochilus melanostigma and Gobius alcockii. Stoliczka found 

 that the typical form eat Crustacea in captivity, but I have no 

 information as to its natural food. 



Relations of the Variety to the Typical Form. 



In order to make this question clear it will be well to commence 

 its discussion by summarizing the resemblances and differences 

 between the two forms {a) as regards their physical structure, and 

 (/^) as regards their habits. 



Physical resemblances between the two forms. 



1. The coloration is practically identical. 



2. The arrangement of the tentacles and mesenteries is the 



same. 



The position of the circular and radial muscles is the same. 

 The structure and nature of the gonads are the same. 



5. Ihe retractor muscles are closely similar. 



