DEVELOPMENT. SI 



An exceedingly interesting case of metamorphosis in an yEginidian medusa has been 

 described by jM'Crady.^ He observed, lying free in the umbrella-cavity of an Oceanidan medusa, 

 to which he gives the name of Tarrifopsk mitricula multitudes of little organisms, presenting various 

 forms, from that of a minute club-shaped hydroid to that of a well-developed medusa belonging 

 to the type of the ^Ej/inida, and all undoubtedly connected with one another as stages of a simple 

 developmental process. 



Though he at first believed these to be the proper offspring of tlie Turrilopsis in which they 

 occurred, he afterwards rejected this notion, and recognised in them the young of a species of 

 Cuiiina {Cuniiia odonaria, M'C), which had selected the umbrella-cavity of tlie Oceanidan in 

 order to spend there as parasites the early stages of their existence. 



The untentaculated, club-shaped larva (the earliest stage observed) was followed by a 

 bitentacular hydroid form with long imperforate proboscis and distinct internal digestive cavity, 

 and he noticed the interesting fact that this bitentacular stage freely repeats itself by budding. 

 Next, two other tentacles make their appearance synuuetrically between those first formed, while 

 the extremity of tlie proboscis seems now to be perforated by a mouth. The umbrella next begins 

 to make its appearance by an annular extension of the circumference of the body close to the oral 

 side of the roots of the tentacles ; and four new tentacles begin to sprout between those already 

 formed, while lithocysts become developed on the margin of the incipient umbrella. After 

 this the larva assumes the form of an adult Cunina in all essential points, except in the pos- 

 session of a long proboscis, like that of a Geryonia, in which stage it leaves the umbrella-cavity 

 of the Turritopsis to spend a free life in the surrounding water. It is only after it has quitted the 

 medusa on which it had been hitherto living as a parasite that it loses its proboscis, and that the 

 digestive cavity thereby assumes the form characteristic of the family of the ^!Erjinidce. M'Crady 

 views this case as presenting an instance of direct development from the ovum, believing that the 

 Cunina originally gained access to the umbrella of the Turritopsis in the condition of a free- 

 swimming planula. 



Fritz Miiller- has given an excellent account of the metamorphosis of a Geryonidan medusa, 

 Liriope cathariensis, Fr. Miiller; and his observations have been confirmed and extended by 

 Haeckel,^ who has described similar metamorphoses in two other Geryonidans, Glossocodon {Liriope) 

 euryhia and Carmarina [Geryonia) hasfata. In all these cases the medusa in its earliest observed 

 condition was found swimming free in the open sea. The youngest medusa noticed presented 

 the form of a minute hyaline gelatinous sphere ; on one point of whose surface was a small 

 pit-like depression closed over by a perforated diaphragm ; and the most striking feature in the 

 subsequent metamorphosis consisted in the development of two sets of peculiar larval tentacles, 

 of which one or botli sets were destined after a period to disappear, their place being supplied by 

 an entu'ely different set, which remained as permanent organs during the life of the medusa. 

 The larval tentacles are solid and rigid, and have no connexion with the gastrovascular system ; 

 while the permanent tentacles are hollow offshoots from the circular canal, and are eminently 

 flexible and extensile. 



While we are entirely ignorant of the origin of the free-swimming bodies which have been 



' Proc. Elliott, ' Soc. Nat. Hist. Charleston, 1856,' p. 55. 



= ' Wiegraann's Archiv,' 1859, p. 310. 



' Haeckel, ' Die Farnilie der Riisselquallen.' 



11 



