MUSEUM OF COMPARATIVE ZOOLOGY. 299 



E. folleata has a liabit of swimming with the bell reversed and the pro- 

 boscis protruded, as shown in Figure 14. This posture is rarely assumed by 

 0. languida. 



Two larval stages in the growth of Epenthesis were observed. Ttie youngest 

 of these has a taller bell than the adult, and seven tentacles with as many oto- 

 cysts. The disposition of the tentacles and otocysts is as follows. Of the 

 seven tentacles six are well developed, while a seventh is a simple enlargement 

 in the marginal border. In each of three quadrants there are two otocysts, 

 and in a fourth there is a single body of this kind. It is to be noticed that 

 the quadrant which contains the beginning of a new tentacle is situated dia- 

 metrically opposite that in which no tentacle is found, and in which there is a 

 single otocyst. In the same way the two quadrants vi^hich bear the fully 

 developed tentacles are opposite each other. This inequality in the number 

 of tentacles and otocysts leads us at first sight to suppose that this form is a 

 monstrosity. There is, however, a certain regularity in the arrangement of the 

 tentacles and otocysts. We are perhaps hardly justified in supposing that in a 

 stage earlier than the present that quadrant which now bears a rudimentary 

 tentacle separating two otocysts had but a single otocyst, and that in larvse still 

 younger we have a medusa with four tentacles and a single otocyst in each 

 quadrant. In this way we may interpret the existence in the present form of 

 a quadrant with a solitary otocyst. 



An older stage * of the medusa than that with seven tentacles is one with 

 eight tentacles, alternating with as many marginal sense bodies. From this 

 stage the adult is formed by the interposition of a new tentacle between each 

 pair already formed, after the formation of an additional otocyst, either by 

 fission from the last, or by a new growth from the beU margin between each 

 pair of tentacles. 



Willia ornata, McCradt. 



Figs. 22 - 24. 



The youngest larva of IF. ornata which was found is very different from the 

 adult. It has a deeper bell and only four tentacles. The bell walls are thin, 

 transparent, and have a smooth surface. There are four narrow, unbranched 

 chymiferous tubes, each of which passes directly from the proboscis to the bell 

 margin. Several specimens of about the same age were taken. In all, the 

 remnant of a communication between the stomach cavity and the hydroid is 

 still visible. There are four short, smooth tentacles,! which are sometimes 

 carried tightly coiled about the base as in Ectopleura. They are also sometimes 

 extended. 



The structures which identify this larva as the young of Willia are four rows 



♦ Both of these stages were fished up in the open sea, and not raised one from 

 the other. 



t According to Mr. Agassiz {op. cit., p. 171), two of these tentacles are longer than 

 the remaining pair. In iny specimens their length was about equal. 



