300 BROOKS. [Vol. X. 



generally stiff and inflexible, primarily solid ; alternation with 

 hydroid polyps not yet known." 



The introduction of a distinction, vouched for by such high 

 authorities, into the text-books has firmly established it, 

 although it is by no means as absolute in nature as it is in the 

 books. 



We see that true endodermal sense-clubs occur among the 

 " Leptolinae," in Laodice and its allies, and that the only 

 difference between them and those of the Trachylinae is the 

 absence of concretions. 



The tentacles of many of the " Leptolinae," of many Euco- 

 pidae, for example, and the accessory tentacles of Laodice are 

 as solid as those of any of the Trachylinae ; and while the 

 fixed hydroid cormus is restricted to the " Leptolinae," a 

 hydra stage of development is, so far as our knowledge goes, 

 common to all the veiled medusae. 



McCrady pointed out in 1857 {GymnopJitJiahnata, p. 108) 

 that the embryo of Cunina octonaria is " a free hydra, like the 

 free stage of Tubularia," and I have shown (TJie Life-History 

 of the Hydro-Medusae) that this is true of the Geryonidae and 

 of all the Trachylinae whose life-history is known. 



The Trachylinae of Haeckel are a natural group, well worthy 

 cf a distinct name, although it is important to emphasize the 

 fact that neither in their structure nor their development do 

 we find them fundamentally different from the other hydro- 

 medusae. 



In this connection we may note, in passing, a point in which 

 Laodice, and in fact many of the campanularian medusae, 

 resemble the Trachylinae. The Hertwigs have shown that the 

 tentacles of the Trachylinae do not spring from the bell mar- 

 gin, but that they are pushed upwards by a thick .pad of epithe- 

 lium so rich in nettle cells that it forms a firm, cartilage-like 

 basis for the tentacle. They also show that the endodermal 

 axis of the tentacle is prolonged inwards above the upper 

 surface of the circular canal. The section of the base of the 

 tentacle of Laodice shown in Fig. 7 shows that it has a well- 

 marked nettle ridge, and that the large endoderm cells of the 

 tentacle preserve their distinctness for some distance inside 



