210 W. K. BROOKS. 



The knowledge of the true structure and mode of origin of the 

 adult cunina which we owe to Wilson's researches, already referred 

 to, proves that the narcomedusse represent an independent and 

 very primitive branch of the craspedota and while I was ignorant 

 of this at the time my memoir was written, and while I then, with 

 all other naturalists, believed the narcomedusae to be much nearer 

 to the hydroids than they really are, I recognized, and thought that 

 I had clearly stated my opinion, that the cormus and the alternation 

 of generations in parasitic cuninas is a secondary and independent 

 acquisition, although I still think, as I did then, that the analogy 

 is most suggestive and instructive, inasmuch as it shows how easily 

 secondary complications, essentially similar to those of hydroid 

 cormi, may be grafted on to the structure of a simple hydra. 



I regret that I am not able to refer to my memoir as I write, 

 for critics of my views have spoken as if I regarded the parasitic 

 cunina-cormus, as the ancestor of modern hydroids. Thus, for 

 example, Maas says, p. 295, that Metschnichoff and Brooks hold 

 that the narcomeduste are primitive forms, and that the alternation 

 of generations of the hydroid jyolfps is derived from that of cunina. 



As far as I myself am concerned, I certainly regard the unmodi- 

 fied cunina metamorphosis as primitive, but I regard the compli- 

 cations which have been introduced by parasitism, as analogous to, 

 but quite independent of, the peculiarities of hydroids. 



A general view of a subject so full of complicated details as the 

 life history of the craspedota is difficult, as illustrations and minute 

 accounts of specific instances are so necessary. I hope, however, 

 that, notwithstanding Lang's verdict (Ueber die Einfluss der fest- 

 sitzenden Lebensweise, p. 159) that it is 'Hhe most improbable of 

 improbabilities" the view that the craspedota owe their origin to 

 pelagic influences will commend itself to those who are most 

 familiar with these animals. 



It is hardly probable, however, that our modern craspedota are 

 primitively pelagic, for their size, the complication of their organi- 

 zation, and especially their great diversity of structure and habits, 

 would seem to show that while they have been evolved in the open 

 ocean, they are not the product of primitive and simple conditions, 

 but that they show the influence of the more intense and compli- 

 cated struggle for existence which has come from competition with 



