HYDROZOA. 



123 



The swimming organ of Pelagia is sub-globose, 

 about three inches in diameter, divided at its 

 margin into sixteen lobes. Under eight of these 

 lobes are seen notches, each lodging a hooded 

 lithocyst, while from the remaining lobes depend 

 an equal number of long, contractile tentacula. 

 A polypite, short and broad, is attached, proxi- 

 mally, to the concave centre of the umbrella; 

 distally, it terminates in four furbelowed lips, 

 which extend to a length of nearly four inches. 

 A number of csecal sacs, corresponding with the 

 lobes of the umbrella, are prolonged from the 

 digestive cavity. In other characters Pelagia 

 resembles the free zooids of Aurelia and its allies 



(fig- 7> &)• 



The Lucernaridce admit of being arranged 

 under two principal sections, in one of which the 

 development is continuous, in the other, discon- 

 tinuous. The first section includes Pelagia and 

 the Lucernariadce, in which reproductive elements 

 are produced by the organism immediately re- 

 sulting from a generative act. In other members 

 of the order, the primitive result of this act is a 

 fixed and sexless ' Lucernaroid,' which gives rise 

 by fission to free zooids of disproportionate size, 

 in which the reproductive organs are developed. 

 The first section, again, includes two minor di- 

 visions, in one of which the umbrella is perma- 

 nently free, in the other, furnished with an organ 

 of attachment. But the developmental cycle of 

 each Lucernarid belonging to the second section 

 presents these two principal forms. 



It is worthy of remark, that the Lucernaroids 

 of very different genera — such as Gephea and 



* 



i 



Ghrysaora 



are often wonderfully alike in struc- 



