SEA-NETTLES. 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 meduse piled on one 
another: they become separated from each other, from before back- 
ward ; and then swim freely away as young medusee?. 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 
erowth—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 Cestwm, 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 KoELLIKeER?, in Stomobrachium mirabile, which 
he believes to be a larval form of Mesonema caerulescens, anew species 
of Medusa discovered by him at Messina. The fission begins in the 
stomach—many individuals having been found with their round 
dise 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 dise 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 Sars Beskrivelser og Jagttagelser &c. (extract from it in WIEGMANN’S Archiv. 
1836, s. 197 &c.); and in Winem. Archiv. 1837, B. u. s. 406; C. T. Von Srepoip 
Beitriige zur Naturgesch. der wirbellosen Thiere, Dantzig, 1839, 4to. s. 26—35. SARs 
in WIEGMANN and Ericuson’s Archiv. 1841, s. 9—34. Mémoire sur le développement 
de la Medusa aurita et de la Cyanea capillata, Ann. des sc. nat. sec. série xvi. Zoologie, 
pp. 321—348, Pl. 15 A—17. 1841. J. Sremnstrue Om Fortplantning og Udvikling 
gqennem vexlende Generationsrakker, Kjébenhavn, 1842, 4to. 
? SIEBOLD and KorLiiker’s Zeitschrift f. wissenschaft. Zool, wv. pp. 325, 327. 
