228 BULLETIN OF THE 



peculiar, but follows the laws of growth so often described in these structures 

 in related genera. 



The cluster of medusa buds is confined to the terminal end of the lateral 

 branches. Near the base of attachment of each bud there is a patch of red 

 pigment. As the medusa grows in size and the proboscis begins to be formed, 

 the shape of the bud gets elongated, cylindrical, and at the same time two 

 opposite tentacles push out on its free margin. The proboscis has a yellow 

 and orange color. The reddish patches of pigment near the base of attach- 

 ment of the immature bell persist even after the medusa has detached itself 

 from its connection with the lateral branches. 



The different layers of the body of the medusa bell (Plate IV. Fig. 4) can 

 be readily seen through its transparent walls. Of these the epiblast, hypo- 

 blast, and intermediate layer can be easily recognized. The origin and growth 

 of the radial tubes, and the subsequent formation of the circular or marginal 

 canal, was traced. This growth does not differ from what has alread}'^ been 

 described in Syncoryne (Sarssia) and several other genera. 



The fish (Seriola) was kept alive in an aquarium for several days, and from 

 the attached hydroid many free medusiform gonophores were raised. On the 

 morning following the day when the fish was captured, many medusae were 

 found in the aquaria, and every day after its capture many specimens ripened 

 from the undeveloped buds, and one by one detached themselves from their 

 union with the gonosome. There is no possibility of a doubt that the free 

 medusa, as here described, has detached itself from the gonosome attached 

 to the body of the fish. 



The free medusa (Plate V. Fig. 1), when it breaks its connection with the 

 gonosome, has two short tentacles situated opposite each other on the bell 

 margin. The medusa bell long before detachment had begun the peculiar ex- 

 pansion and contraction which precede separation, and when once free moves 

 gaily about in the surrounding water. Shortly after its detachment, the me- 

 dusa with two tentacles resembles a young Stomatoca.* The structure of the 

 Hydrichthys medusa just escaped from its attachment to the gonosome is as 

 follows. 



The bell is oval, without apical projection, and recalls in outline that of 

 Sarsia. The onter surface is dotted with numerous nematocysts.f Bell walla 

 colorless and transparent. There are four broad radial vessels and a marginal 

 tube. The tentacular bulbs are reddish, without ocellus. Two tentacles arise 

 from tentacular bulbs diametrically opposite on the bell margin. No otocysts 

 on the bell margin. The proboscis is cylindrical, of an orange and yellow 

 color. There are patches of red pigment near its attachment. The mouth is 

 simple, with entire margin destitute of appendages. 



* The fact that Stomatoca ie a medusa of Perigonimus was pointed out by 

 Haeckel, Allman, Hincks, and others. 



t These nematocysts are most prominent in younger stages in the growth of 

 the medusa. Tliey are well marked even before the medusa form is attained. 



