302 BROOKS. [Vol. X. 



among the campanularian medusae the ocellate forms are the 

 most primitive and generalized. 



A. Agassiz says of the hydroid (Lafoea) of Laodice calcarata 

 {N. Amer. Acalephae, 1865, p. 125): "The sterile individuals 

 recall the Tubularians, as do in fact all the Sertularians. . . . 

 The Medusae {young medusae ?) of this Sertularian-like Hydro- 

 medusarians resemble more those of the Tubularians than those 

 of the Campanularians. The vertical diameter of the {young) 

 Medusae is greater than the transverse; the bell is of moderate 

 thickness, the abactinal part being slightly conical; the diges- 

 tive cavity is short, and consists of four simple lobes, giving 

 the actinostome the shape of a cone. When it escapes from 

 the reproductive calycle it has only two long tentacles, two 

 slightly developed ones, and four more hardly perceptible in 

 the middle of the space between the four chymiferous tubes." 



The Hertwigs {Nervensystem und Sinnesorgane der Medusen, 

 1878, p. 155) also hold that "we must regard the Laodiceidae 

 and Melicertidae as more lowly organized than the other 

 Vesiculatae (campanularian medusae), and nearer the com- 

 mon type from which the Vesiculatae (campanularian medu- 

 sae) on the one hand, and on the other the Ocellatae 

 (tubularian medusae), have been developed." 



Haeckel shares this opinion, and tells us {System der Medu- 

 sen, p. 121) that "we find among the Laodiceidae, in the 

 genus Tetrancma especially, the primitive type from which the 

 Leptomedusae (campanularian medusae) have been developed." 



Authorities are agreed then that while the ocellate campanu- 

 larian medusae are distinctly in the campanularian line they 

 are very low down in this line, and still retain features which 

 they have inherited from the unknown common ancestor of 

 both tubularians and campanularians. 



The occurrence among them of endodermal sense clubs is 

 another generalized feature which they share with the Lepto- 

 linae. The Tubulariae, the Sertulariae, and the Leptolinae 

 must therefore be regarded as divergent descendants of an 

 ancestor more primitive than any known hydroid or veiled 

 medusae, and it is clear that we cannot derive the Leptolinae 

 from any known hydroid. 



