Mr Cobb, On fresh-water New Zealand Nematodes. 363 



Free-living fresh-water New Zealand Nematodes. By N. A. 

 Cobb, with note by K. Lucas, B.A., Trinity College. (Commu- 

 nicated by Mr A. E. Shipley.) 



[Read 1 February 1904.] 



The Nematodes whose descriptions follow are of some little 

 interest in the following particulars. 



In view of the few species at present known from New Zealand 

 it is of interest to see that all the present ones belong to well 

 known genera, and that as species they present no remarkable 

 variations from the normal types of their respective groups. This 

 leads us a step further towards the belief that many of the 

 Nematode genera living free in the soil and in water will be found 

 to have a very wide geographical distribution. This is precisely 

 what was to be expected from what we know of the life histories 

 in a number of these genera. The small size of the individuals, 

 their fecundity, their adaptability to transportation by a great 

 variety of agencies, and their resistance to desiccation, at least in 

 certain stages of their existence, are all in favour of wide dis- 

 tribution. 



The depths from which some of the present specimens were 

 dredged throws an interesting light on the fauna of such depths. 

 There have been comparatively few Nematodes taken in fresh 

 water from such depths. That all the species thus taken should 

 belong, in the present instance, to known genera and be closely 

 related to known species indicates that even very considerable 

 changes of environment effect small changes in the form of these 

 worms. 



That all the species here presented are for the most part of 

 large size may be an idiosyncrasy of the collector, an effect of the 

 apparatus used, or a mere coincidence, and hence little weight can 

 be attached to the fact. 



So far as I can see the species resemble most closely other 

 austral species, though some of them are certainly closely like 

 those of Europe. The Mononchus rex finds its closest known 

 relative in Fiji, while the Dorylaimi are most closely related to 

 Australian species. 



The fact that the two species of Dorylaimus dredged from 

 New Zealand lakes should belong one to the North Island and 

 the other to the South Island may be indicative of variation from 

 a common stock, especially as the species appear to be closely 

 related. The localities from which the two species are derived are 

 six to eight hundred miles apart on a north and south line, and 

 hence the differences in climate are considerable. 



There is no clue to the host of the species of Mermis. The 

 discovery of a species of Mermis at such a depth living free in 

 fresh water is rather interesting. 



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