SEA-XETTfcE3V 101 



seen, round which at first two, then other two projections appear 

 that become lengthened out into arms. Soon there grow out four 

 other similar arms, and the animal has then the form of an eight- 

 armed Polyp. These arms can shorten and lengthen themselves 

 greatly. In this state the animal continues several months, and 

 can multiply itself by buds and offsets. Subsequently there come 

 into view transverse indentations, by which the animal is divided 

 into several rings resting upon one another, round each of which 

 eight rays arise. These rings are like young medusae piled on one 

 another : they become separated from each other, from before back- 

 ward ; and then swim freely away as young medusae 1 . How long a 

 period is requisite for their full growth is unknown. The genital 

 organs could not be distinguished until they were more than an 

 inch in size. Hence it is clearly an error when some ascribe to 

 these creatures in general a very short duration of life and a rapid 

 growth or even name them annual animals. Their power of re- 

 production seems to be very small. Some species are able to bear 

 the loss of parts, but these when removed do not continue to grow. 

 In the genus Cestum, however, MERTENS was led to believe, from 

 some observations which he was unable to complete, that propaga- 

 tion by spontaneous division may be admitted. [And this has been 

 lately confirmed by KOELLIKER 2 , in Stomobraohium mirabile, which 

 he believes to be a larval form ofMesonema ccerulescens, a new species 

 of Medusa discovered by him at Messina. The fission begins in the 

 stomach many individuals having been found with their round 

 disc somewhat elongated and with two stomachs more or less com- 

 pletely separate by constriction, but still lying side by side. Next, 

 a meridional groove is seen on the outside of the disc between the 

 stomachs : it deepens gradually until the acaleph is separated into 

 two distinct individuals. The whole process may be completed in 

 eight to twelve hours. The multiplication however is not yet 



1 SAKS Beskrivelser og Jagttagelser &c. (extract from it in WIEGMANN'S ArcJiiv. 

 1836, s. 197 &c.) ; and in WIEGM. Archiv. 1837, B. n. s. 406 ; C. T. VON SIEBOLD 

 Btitrage zur Naturgesch. der wirbellosen TMere, Dantzig, 1839, 4to. s. 26 35. SAKS 

 in WIEGMANN and ERICHSON'S Archiv. 1841, s. 9 34. Memoire sur le dtveloppement 

 de la Medusa aurita et de la Cyancea capillata, Ann. des sc. not. sec. se"rie xvi. Zoologie, 

 pp. 321 348, PI. 15 A 17. 1841. J. STEENSTRUP Om Fortplantning og UdviMing 

 gjcnnem vexlende GenerationsrdkJcer, Kjobenhavn, 1842, 4to. 



3 SIEBOLD and KOELLIKER'S Zeitschriftf. wissenscfarft. Zool. iv. pp. 325, 327. 



