244 HYDROIDiE. Part IV. 



of the breeding season. The head has, in every respect, truly the character of 

 all the Tubularidae, but may be more closely compared to that of Parypha 

 (PI. XXIII. Fig. l*"). At the height of the breeding season in January, the whole 

 disk between the coronal tentacles (PI. XXV. Fig. 2, f) and the proboscis {1} f) 

 is crowded with the medusoid progeny {d e), in all stages of growth, from the 

 merest incipient buds to their fully-developed state {d d^), in which they drop from 

 the parent. 



The horny sheath {Figs. 2 and 3, a^) is a very notable feature in this genus, 

 as it shows a tendency to form a permanent, turbinate terminal expansion, more 

 or less deeply constricted at several successive points, so as to have the appearance 

 of being ringed. The substance of the sheath, at the upper end, is rather filmy, 

 and very delicate, yielding readily to the distension and flexure of the stem. 



The free Medusa {Figs. 14, 14*, 15, and 15*) of our Hybocodon, bears a very 

 close resemblance to that of Coryne fritillaria, as figured by Steenstrup in his 

 work upon alternate generation (PI. I. Figs. 41-45), but the Hydroid represented 

 as the parent stock of the latter is a Coryne-like animal, if we may judge from 

 the very small figure given by that author.^ 



Hereafter we shall give a full description of our Medusa; for the present we 

 must return to the Hydroid, in order to present a more detailed account of its 

 structure. The proboscis carries two rows of tentacles (PI. XXV. Figs. 2, 2% and 

 3, f f), one of which {f) borders closely upon the mouth {Fig. 2*, p), while the 

 other is placed at a short distance below, in such a manner that the tentacles of 

 this row alternate with those of the terminal circle. When the proboscis is strongly 

 contracted the two rows are oftentimes brought, apparently, into one series {Fig. 3, 

 f f), but it may be readily seen that the one is concentric to the other. In the 

 oldest hydroids we have counted as many as thirty-two buccal tentacles {Fig. 3), 

 and, as they alternate with one another, there are sixteen in each row. They 

 differ in nowise, as regards shape, from those of other Tubularida? ; but those of 

 the terminal circle {Figs. 2 and 2% f) are only half as long as those of the second 

 series {f) ; and the decurrent bases {Fig. 2% p^) of the latter alone form the 

 broad, parallel ridges, which lie closely, side by side, about the circumference of 

 the proboscis. The rest of the head, the disk which bears the medusaa, and iipon 

 which the coronal tentacles are based, have the same general structure as in 

 Paryi^ha. The bunches of medusae, which are present from January to April, are, 



* It is very questionable whether the Steen- Hydroid because of a general resemblance to the 



strupia-like Medusa figured by Sars is truly the medusoids which were attached to it. It is un- 



progeny of Coryne fritillaria, inasmuch as he found fortunate that he did not give magnified figures 



it floating in the open ocean, and refers it to this of the latter. 



