835 



of the mouth. The second kind is homologous with the prehensile 

 organs of the Diphydae and Physophorida}, and with the peculiar 

 clavate processes of Plumularia, Ail these organs commence their 

 development as bud-like processes of the two joining membranes. 

 The peculiar clavate organs of Plumularia are developed from the 

 common tube independently of the stomach. They have not been 

 hitherto described, and were observed by the author in two species 

 of Plumularia dredged at Port Curtis. They were of two kinds, the 

 one attached to the cell of the polype, the other to the pedicle of the 

 ovary. To each species there were three processes of the former 

 kind, two above proceeding from near that edge of the aperture 

 which is towards the stem, the other below from the front part of 

 the base of the cell. They were conical in one species, club-shaped 

 and articulated in the other, and consisted of an external horny 

 membrane open at the apex, and an internal delicate membrane in- 

 closing a cavity, all these being continuous with the corresponding 

 parts of the stem. At the apex of each, and capable of being pressed 

 through the aperture, lay a number of thread-cells. The second 

 kind of organ was present in the species with conical processes. It 

 consisted of a stem proceeding from the pedicle of the ovary, bearing 

 a series of conical bodies, having the same constitution as those just 

 described ; the whole bearing a close resemblance to the prehensile 

 organs of the Diphydae. 



The following table exhibits the homologies of the several families, 

 which must be regarded as by no means so distinct as hitherto sup- 

 posed, but rather as members of one great group, organized upon 

 one simple and uniform plan, and even in their most complex and 

 aberrant forms reducible to the same type. 



Stomachs identical in Structure throughout. 

 Medusa. Physophorida. Diphydce. Sertularidce. Hydra. 



Disc Natatorial organ Natatorial organ. 



Canals { Canals of natatorial 1 Canals of natatorial 



I organ J organ. 



Common cavity . . 1 , c i j 



Canals of branches )-Common tube ..-..( Sacculus and com- 1 ^avitv of stem. 



{RMz.) J montube / 



Bract Polype-cell. 



Tentacles, 1 {^"tt^^^ Oval tentacles. 



2 Prehensile organs Clavate organs Tentacles (?). 



r Generative sac Generative organ.. . Generative organ. 



Generative organs < Natatorial organ of\ j Natatorial organs 



I. generative sac ../ I (Coryne). 

 Marginal vesicle ? ? ? 



2. " Memoir to accompany a Map of the Magnetic Variation for 

 IS^O in the Atlantic Ocean between the parallels of 60° N. and 

 60° S. latitude, being Contributions to Terrestrial Magnetism, No. 9." 

 By Lieut.- Colonel Edward Sabine, R.A., For. Sec.R.S., and printed 

 in the Philosophical Transactions. 



In this Number of the Magnetic Contributions the author gives 

 maps of the Magnetic Declination in the Atlantic in January 1840, 

 between the parallels of 60° N. and 60° S. lat., founded on 1480de- 



3 



