198 JOURNAL OF SCIENCE 
the less radical will be the change. We can, therefore, under- 
stand why the zoea of the walking animal, such as the crab, 
would develop protective apparatus; while the zoea of the 
rapidly-swimming macruran would acquire organs of flight. We 
have, therefore, an explanation of the two facts that the larvz of 
the greater groups exhibit a certain unity, while within a given 
genus the different species may widely vary. 
ON THE NEW ZEALAND DIPTEROUS FAUNA. 
BY C, R. OSTEN SACKEN, 
(Communicated by Prof, F, W. Hutton). 
The interest connected with the New Zealand fauna, 
especially as regards its origin and affinities, encourages me to 
contribute my mite towards that subject. 
Our knowledge of the Diptera of New Zealand is, as yet, 
very limited. There are about 120-130 published species, and a 
certain number of unpublished ones may be seen in almost every 
European Museum. I have formed, from different sources, but 
principally from the contribution of Mr. Helms, in Greymouth, 
a small collection of about 80-90 species, many of which are not 
yet published. 
Although it would seem premature, from such meagre ma- 
terials, to draw conclusions concerning the affinities of the fauna, 
still there are methods of enquiry that are safe enough even under 
such circumstances. Small collections, formed at random in 
different parts of the country, by persons not especially interested 
in Dipterology, will necessarily contain the most common forms ; 
and if such collections again and again bring up the same species, 
or at least the same genera, we may safely draw the conclusion 
that such species or genera are characteristic of the fauna. The 
inference would be less safe, if the collections were formed by a 
practised dipterologist, as he would generally have a preference 
for some families, at the expense of others. The comparison of 
such common, characteristic forms with corresponding forms, 
obtained under similar conditions, in another fauna, affords a 
trustworthy starting point for defining the composition of these 
faunas. 
Now what strikes me at once in scanning my small New 
Zealand collection, and mentally completing it with the data of 
the published catalogues, is the abundant presence of groups 
which would hardly be represented at all in collections formed 
under similar conditions in the regions of Europe or of North 
America. 
There is the group of Beride, represented in Central Europe 
by 7 or 8 species ; small flies, distantly related to Stratiomyide; 
they usually occur among bushes, and in the shadowy parts of 
