Miscellaneous. 349 



Thus the egg of a Medusa, in such cases, does not produce a Me- 

 dusa, except after going through the intermediate state of a polyp. 

 Or if we commence with the polyp, the series is thus : — 



1 . The polyp produces bulbs that become Medusae ; 



2. The Medusae produce eggs ; 



3. The eggs produce polyps. 



This is what is called by Steenstrup " Alternation of Generations ;" 

 and he considers the earlier generation as preparing the way for the 

 latter. It certainly seems to be a most mysterious process : — a pa- 

 rent producing eggs which afford a progeny of wholly different form 

 (even so different, that naturalists have arranged the progeny in an- 

 other grand division of the Radiata) ; and this progeny, afterwards, 

 by a species of budding or gemmation repeating the form of the ori- 

 ginal parent. 



Yet although seemingly so mysterious, is not this mode of deve- 

 lopment common in the vegetable kingdom ? Is it not the prevalent 

 process in the plants of our gardens and fields, with which we are all 

 familiar ? 



It is well known to us, that in most plants, our trees and shrubs 

 for example, growth from the seed brings out a bud of leaves ; from 

 this bud after elongation, other leaf-buds are often developed, each 

 consisting like the first of a number of leaves. It is an admitted fact 

 (as may be found in Treatises on Vegetable Physiology) that each of 

 these buds is a proper plant-individual, and that those constituting a 

 tree are as distinct and independent as the several polyps of a com- 

 pound zoophyte ; and that the tree therefore is as much a compound 

 group of individuals as the zoophyte. In some cases the plant forms 

 but a single leaf-bud ; in others, where there is successive gemmation 

 for a period, the number is gradually multiplied, and more or less ac- 

 cording to the habit of the species. So among polyps, there is the 

 simple and compoimd Tubularia, Campanularia, and the like. 



After the plant has sufficiently matured by the production and 

 growth of its number of leaf-buds, there is a new development — a 

 flower-bud — consisting of the same elements as the leaf-bud, but 

 wholly unlike it in general appearance — as much so, as the Medusa 

 is unlike the polyp. The flower-individual starts as a bulb from the 

 leaf-individual, or the group of leaf-individuals, and is analogous in 

 every respect to the bulbs from the Campanularia; and alHed species ; 

 and when it has fully matured, it produces, like the Medusa, ovules 

 or seed — these seed to begin the round again of successive or alter- 

 nating developments. 



Thus among plants the seeds produce leaf-individuals ; these yield 

 bulbs or buds becoming flower-indi%dduals ; and these produce seeds ; 

 precisely as the egg produces polyps, the polyps, bulbs that deve- 

 lope into Medusae, and the Medusae, eggs. 



When we follow out this subject minutely, we find the analogy 

 completely sustained even in minor points of structure and growth. 

 The leaf-bud consists of leaves developed in a spiral order ; and in the 

 polyp, as some species show beyond doubt, the tentacles and corre- 

 sponding parts are spiral in development. The same spiral character 



