40 A JOURNEY IN BRAZIL. 
will be difficult and often impossible in travelling, we must 
at least get the nests of ants, bees, wasps, and the like, in 
order to ascertain all we can respecting their communities. 
When these are not too large it is easy to secure them by 
slipping a bag over them, thus taking the whole settlement 
captive. It may then be preserved by dipping into alcohol, 
and examined at leisure, so as to ascertain the number and 
nature of the individuals contained in it, and learn some- 
thing at least of their habits. Nor le' us neglect the do- 
mestic establishments of spiders. There is an immense 
variety of spiders in South America, and a great differ- 
ence in their webs. It would be well to preserve these on 
sheets of paper, to make drawings of them, and examine 
their threads microscopically." 
April 21s. Yesterday Mr. Agassiz gave his closing 
lecture, knowing that to-day all would be occupied with 
preparations for landing. He gave a little history of Steen- 
strup and Sars, and showed the influence their embryologi- 
cal investigations have had in reforming classification, and 
also their direct bearing upon the question of the origin of 
species. To these investigators science owes the discovery 
of the so-called "alternate generations," in which the Hy- 
droid, either by budding or by the breaking up of its own 
body, gives rise to numerous jelly-fishes ; these lay eggs 
which produce Hydroids again, and the Hydroids renew 
the process as before.* 
" These results are but recently added to the annals of sci 
* As these investigations have been published with so much detail (Steen 
strup, Alternate Generation, Sars's Fauna Norwegica ; L. Agassiz, Contr. t( 
Nat. Hist, of U. S.), it has not been thought necessary to reproduce this par* 
of the lecture here. Any one who cares to read a less technical account of 
these investigations than those originally published, will find it in " Methods 
of Study," by L. Agassiz. 
