89 



the tentacles wMcli then may make their appearance, at whatever 

 point of the circumference it may be, and however irregularly they 

 may divide the existing spaces between the tentacles, would be the 

 tentacles of the third set, and so on for the other tentacles. Although 

 in some of the families, as the Laodicece Ag., the Eucopidce Gegenb., 

 the Nucleiferce Less., the Melicertidce Ag., I have found that the 

 order of appearance of the different tentacles coincided with the 

 order of appearance of the chambers of Polyps ; yet the exceptions 

 to this law were numerous, as in the Tuhularidce Ag., the Bougain- 

 villidce Lute, the Nemopsidce Ag., the Berenicidoi Esch. In one 

 and the same family we find genera in which the law holds good, 

 while in closely-allied forms the order of development is materially 

 modified, as is the case in Clytia and in Tiaropsis. 



Another great difference between the Polyps and Acalephs is the 

 great variety of numbers which are found in the tentacles of the first 

 set in Acalephs, while in Polyps six is almost uniformly the number 

 of chambers of the first cycle. In Acalephs, on the contrary, we find 

 in some Eucopidce sixteen, Obelia (fig. 5), in others, Eucope (fig. 7), 

 twenty-four, and forty-eight (fig. 6), as the number of tentacles of the 

 first set ; in the Oceanidce Esch., as limited by Agassiz, there are four 

 in Clytia (fig. 14:),Eucheilota (fig. 16), and Tiaropsis (fig. 10) ; in the 

 Laodicece, there are four in Staurophora (fig. 1), and two in LapJicea 

 (fig. 4). Among the Berenicidce there are four (see Willia) ; the 

 Nemopsidce have sixteen (fig. 26), while the Bougainvillidce have eight, 

 as in Bougainvillia (fig. 24), or four as in Lizzia (fig. 28). In some 

 of the Tubularians, as in Corymorpha (fig. 31), and Hybocodon (fig. 

 30), the first set has but one tentacle. This shows, among the few 

 Medusae which I have examined, a greater variety of modes of de- 

 velopment than we find in the whole class of Polyps, as far as they 

 are known. 



In Staurophora laciniata Ag., I have followed this succession of 

 the sets of tentacles as far as the seventeenth set. The first set con- 

 sists of four tentacles, and perhaps only of two if we may form con- 

 jectures from the young Medusa of Laplioea mentioned below. In 

 Fig. 1. fig. 1 we have a young Staurophora, 



measuring about -^^ of an inch across the 

 circular tube, in which the second set of 

 tentacles is developed. The digestive 

 cavity hangs down as a short proboscis ; 

 there are no ovaries developed. The 

 Y^HJ^^TsST^A^TriaciS^ formula of the tentacles for a quarter 

 magnified 10 diam. segment, at the stage of growth of fig. 1, 



could be represented by T;^, t^, T^; — T^^, T^^, being the tentacles 

 of the first set, placed in the prolongation of the chymiferous tubes. 



