13 



divisions, but in consequence of their organization being so much 

 higher the independent existence so produced is not at once per- 

 fect, but becomes so in a few days. Those who have kept the 

 Actinise in Aquaria know how commonly they split into one or 

 more pieces, and after the lapse of a few days each fragment be- 

 comes a perfect Sea Anemone. Mark, however, that more time 

 is necessarily consumed in the production of the adult form when 

 independent existence is commenced in an imperfect state. 



In the other division of the Coelenterata, the Hydrozoa, the 

 element of time becomes very important, because many of the 

 species pass through a metamorphosis, or alternation of generation ; 

 to describe the mode of reproduction in the Hydrozoa would be 

 quite impossible within the limits of this address. Those mem- 

 bers who may wish to understand the subject should consult Pro- 

 fessor Allman's monograph of the Gymnoblastic Hydroida, a 

 copy of which is in our library. 



Turning to the Annulosa and selecting the Insecta for con- 

 sideration. 



How short a time it takes to develope some of the low forms 

 of insects all who have gardens know very well. 



In Spring the winged males and females of the Aphids appear; 

 one or two may be seen resting on the young shoot of a rose ; in 

 a few days the solitary specimen has produced hundreds and 

 even thousands of young, generation after generation appearing, 

 and the leaves and stem of the shoot becomes entii-ely concealed 

 by wingless Aphids, which often go through nine or even more 

 generations in a few weeks. 



Amongst the higher Insecta it is by no means unusal for one 

 brood only to be produced in the year ; but it generally happens 

 that the species is dormant during a great part of the year, either 

 in the egg, larva, pupa, or imago form. 



It must also be observed, that in cases of insects of the higher 

 orders, that the life of the individual commences with the egg 

 which contains at first almost no organization, but is entirely self- 

 dependent from the moment of exclusion ; therefore, to make any 

 comparison between the length of time required to develope an 

 insect and a mammal, the foetal life period of the latter must be 

 taken into consideration. 



I shall now pass on to the Vertebrates. 



The lowest order, the Fishes, contains numbers of species which 

 have no definite adult size, but so long as they are supplied with 



