Chap. IV. . HYBOCODON PEOLIFER. 



247 



even though direct evidence is wanting upon this point. I have ah-eady expressed 

 my conviction (p. 217) that some of the Meduste referred to Sarsia are likely to 

 prove to be the offspring of Tubulariaj, rather than of Coryne ; and if this is the 

 case, it will appear, not only that Hydroids which are generically identical produce 

 Medusae exhibiting congeneric characteristics, but also that the genera of well- 

 defined families agree, in their hydroid as well as in the medusoid state, with 

 one another, in those structural relations which determine their form. A com- 

 parison of Tubularia and Corymorpha with the genera described in this chapter, 

 under the names of Hybocodon, Parypha, and Thamnocnidia, shows them to agree 

 in form, or, in other words, to belong to the same family, while they are generi- 

 cally distinct; and so do their free medusa, as far as they are known. Tubularia 

 Dumortieri forms another distinct genus, to which one of the American species 

 belongs. 



Embri/ologi/. — The mode of development of the medusa;, from the first budding 

 of the double-walled hernia {Fig. 4) to the formation of the radiating tubes {Fig. 5, 

 c c"), and the subsequent appearance of the proboscis {Fig. 11, d), and the uniting 

 of the radiating tubes to form the circular canal {b% is identical with that o°f 

 Coryne (PI. XVIII. Figs. 1-12), which we have described so fully in a previous 

 chapter (p. 192). We will not repeat what has been there stated, but simply 

 referring to it, proceed to point out the peculiarities of this genus. About the 

 time that the radiating tubes have developed through four fifths of the depth of 

 the disk {Fig. 6), one of their number pushes out laterally, and carrying the outer 

 wall along with it, forms a hernia {<»). This hernia continues to grow, until 

 it projects so as nearly to double the transverse diameter of the disk {Fig. 7). 

 and its walls {b^ c") are fully twice as thick as in other parts of the body, when 

 a second hernia (near c") begins to push out from the side of the first, at a point 

 corresponding to the end of the radiating tube. The second hernia, developing 

 in size {Fig. 8, h% forms a second sinus in the radiating canal, and then is soon 

 followed by another hernia {Fig. 9, b% which rises between the primary one and 

 the disk, and at the same time the first diverticulum {c^) has more than doubled 

 the transverse diameter of the disk. Soon a third {Fig. 10, P) and a fourth {a}) 

 hernia appear, successively, near to the disk, whilst the first one (c) becomes 

 elongated into the fashion of a tentacle, which is solid at the distal half As 

 the first medusa continues to develop, the primary hernia, with its tentacle {Fig. 

 11, g), elongates at a corresponding rate, and the second, third, and fourth hernia 

 show their medusoid character by the development of radiating tubes {f f\ whilst 

 other hernifB arise at the base of the primary one. Hardly have the second, 

 third, and fourth medusa fairly formed their tubes before each one begins to 

 exhibit a one-sided protrusion from the radiating canal, identical with that noticed 



