296 COELENTERATA HYDROZOA chap. 



In Ciinina prohoscidea, and in some other species, a ^eiy 

 remarkable method of reproduction has been described hj 

 Metschnikoff, called by him " sporogony." In these cases young 

 sexual cells (male or female) wander from the gonad of the 

 parent into the mesogloea of the umbrella, where they develop 

 parthenogenetically into ciliated morulae. These escape by the 

 radial canals into the gastric cavity, and tliere form a stolon 

 from which young Medusae are formed by gemmation. In C. 

 proboscidea these young Medusae are like the genus Solmaris, but 

 in C. Thododactyla they have the form of the parent. In some 

 cases the ciliated larvae leave the parent altogether and become 

 attached to a Geryonia or some other ^Medusa, where they form 

 the stolon. 



This very interesting method of reproduction cannot be re- 

 garded as a primitive one, and throws no light on the origin of 

 the order. It might be regarded as a further stage in the 

 degeneration of the hydrosome stage in its adaptation to a, 

 parasitic existence. 



The Narcomedusae have a wide geographical distribution. 

 Species of Aeginopsis occur in the White Sea and Bering Strait, 

 but the genera are more characteristic of warmer waters. Some 

 species occur in moderately deep water, and Cunarcha was found 

 in 1675 fathoms off the Canaries, but they are more usually 

 found at or near the surface of the sea. 



Fam. Cunanthidae. — Narcomedusae with large gastral diver- 

 ticula corresponding in position with the bases of the tentacles. 

 Cunina and Cunoctantha, occurring in the Mediterranean and 

 in the Atlantic and Pacific Oceans, belong to this family. In 

 Cunina the tentacles may be eight in number, or some multiple 

 of four between eight and twenty-four. In Cunoctantha the 

 number of tentacles appears to be constantly eight. 



Fam. Peganthidae.— There appear to be no gastral pouches 

 in this family. The species of Pegantha are found at depths of 

 about 80 fathoms in the Indian and Pacific Oceans. 



Fam. Aeginidae. — The large gastral pouches of this family 

 alternate with the bases of the tentacles. Aegina occurs in the 

 Atlantic and Pacific Oceans. Aeginopsis. 



Fam. Solmaridae. — In this family the gastral pouches are 

 variable, suiiu'timcs corresponding with, sometimes alternating 

 with, the bases of the tentacles. The circular canal is represented 



