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grades of perfection, and that a series of intermediate forms 

 connects the simple open velar pouch of Mitrocoma with the 

 closed vesicle of Aequorea. 



Inasmuch as these organs are restricted to the higher mem- 

 bers of the group, " Vesiculatae," and here form a progressive 

 series, and as the group is a homogeneous and natural one, 

 they hold it probable, p. 154, that the ectodermal marginal 

 sense organs are not actually absent in the lower forms, but 

 that they are probably present in a condition so simple and 

 primitive that they have been overlooked. 



A very similar opinion was advanced in 1857 by McCrady 

 who suggests "the probability from the analogy of Thaumantias 

 and Tiaropsis with Eucope, that these ocellate species will be 

 found characterized by such marginal capsules " during their 

 younger stages. 



The Hertwigs say, however, that this is not the only alter- 

 native, for it is possible, although they do not think it probable, 

 that these simple and primitive medusae may, at the present 

 day, be in the condition which prevailed before the first trace 

 of marginal vesicle was acquired. 



My studies of Laodice show that neither of these alterna- 

 tives holds true, but that we have, in its well-known marginal 

 clubs, sense organs of a type which, according to the books, 

 never occurs in campanularian medusae. 



Laodice is neither without marginal sense organs nor does it 

 present incipient stages in the evolution of ectodermal sense 

 vesicles. 



It has sense organs of very simple and primitive structure 

 but they are not velar, nor ectodermal, nor are they connected 

 with the lower nerve ring. They are endodermal, they spring 

 from a nerve ring above the velum, and they are identical in 

 all their anatomical relations with the sense-clubs of the Narco- 

 medusae and Trachomedusae. 



They are minute transparent clubs, attached by slender but 

 rather stiff stalks to the bell-margin and they are well shown 

 in Fig. I. This is an oral view of a Laodice from the Bahama 

 Islands. It has thirty-two large primary tentacles, each with a 

 basal bulb and a large black ocellus ; alternating with these are 



