igoy.] Records of tlie I ndian Museu))i. 71 



all in consequence having a considerable external resemblance both 

 to one another and to the form under consideration. 



The differences which the two forms of M . schillerianum exhibit 

 as regards their muscles and mesenteries are perhaps of more 

 importance, from the point of view of the systematist, than the dif- 

 ferences in the general appearance and shape of the animals. The 

 muscular differences, however, all seem to be what may be called 

 rather d3'namical than morphological. The position of the muscles 

 as regards the layers of the body is identical in the two forms, 

 but in var. exul they appear to have become strengthened in cer- 

 tain directions and weakened in others, in accordance with a com- 

 plete change in the mode of life. Although the mesoderm of the 

 mesenteries is much thinner in the new than in the typical race, 

 and the secondarj^ mesenteries are in a much earlier stage of de- 

 velopment as regards their whole form and structure, I think that 

 a similar explanation is possible, for this change is, like that of the 

 muscles, one of development. The mesenteries have not evolved 

 new characters in the isolated race but remain throughout life in 

 a condition through which the}^ pass at an early age in the tj^pical 

 form, and it is obviously a convenient condition as regards the 

 bionomics of the race. This explanation does not quite apply to 

 the thinness of the mesoderm in mesenteries which are just as long 

 as they are in the typical form of the species ; but seeing that one 

 of the most striking biological modifications of the isolated race is 

 the use to which it puts the liquid contained in its ccelenteric 

 cavity, it is not difficult to see that the pressure of this liquid 

 must have, in the case of the individual, considerable influence on 

 the growth of the mesenteries. 



It is noteworthy that those structures which have the same 

 function in the two forms have undergone ver}- little change in 

 the isolated race. This is particularly true of the tentacles and 

 stomodaeum. Indeed, the last-named structure offers so little of 

 interest in connection with the special line of study embodied 

 in this paper, that I have bareh^ referred to it except in the brief 

 systematical description of the two forms. I ought to say, however, 

 that while it is actually longer in the case of a full-grown example 

 of var. exul than it is in one of the typical form of the species, 

 the elongation is by no means proportionate to that of the columns 

 as a whole. The reduction in the number of tentacles and mesen- 

 teries exhibited b}^ the isolated race, is clearly related to its narrow, 

 elongated form. 



In dealing with the question of the modifications which the 

 Actinian of the Port Canning ponds has undergone, it is not by any 

 means easy to apportion the degrees in which these modifications 

 have affected {a) the individual and (&) the race. It is known 

 that individuals of the same isLmily [e.g., in S agar ti a troglodytes) 

 have lived for over fifty 3^ears (see Ash worth and Annandale [9]), 

 but such instances, as Hickson (11) has recently pointed out, 

 are only known in the case of captive specimens, which have re- 

 ceived regular food and lived a sheltered life. Considering the 



