222 Transactions.— Zoology. 
deposit of a few feet in thickness has accumulated. It is evident from this 
that the gravel bed acts as both inlet and outlet, as it drains and filters the 
water from the high lands to the north of the lake, and carries it down to 
keep the water of the lake both pure and at a permanent level. When the 
lake is full, as it always is, the weight of water in it regulates the supply to 
compensate exactly for what has passed away through the gravel-stratum 
and been lost by evaporation. It will thus be seen nature has supplied the 
lake with what is, to all intents and purposes, a “ ball-cock,” and has 
further placed it just where it can be best utilised by the people of Wan- 
ganui as a source of water supply. I may mention, in support of my 
hypothesis as to the supply and drainage of the lake, that, where the blue 
clay bed is exposed on the sea-beach, water flows continually from the over- 
lying gravel. 
Returning to the question whether eels can exist without free access to 
the sea, I may mention that, in Australia, I have caught them in swamps 
and lagoons hundreds of miles from the sea, and utterly cut off from any 
possible communication therewith. It is, therefore, plain that there are 
other reasons than those advanced by Messrs. Travers and Maling, why 
eels cannot live in the localities they mention. It is more likely that low — 
temperature of the water isthereal cause,aseels are notoriously fond of warm, 
sluggish water, not that the water of Lake Virginia partakes of that charac- 
ter, being always both cold and pure ; but even in Lake Virginia they can 
escape extreme cold by burying in the mud at the shallow end ; that they 
do so is more than probable, as during very cold weather they are seldom 
seen or caught in the lake. There is one thing quite certain, they cannot 
leave the lake, which is quite sufficient to controvert the theory of their 
being unable to exist without having access to the sea, 
Art. XXXI.—On the Habits of the Trap-door Spider. 
By R. Gituims. 
[Read before the Otago Institute, 14th September, 1875.] 
Plates VI., VIL., VIII. 
Preface. 
Tuenx are always two departments in the domain of Natural History, the 
one, that of observation and collection in the field, the other that of classi- 
fication and description in the study. The cabinet naturalist undertakes 
the latter, and by his microscope examines and reveals the various functions 
the different parts of the animal, their relation to one another, and to 
other species; measures, records, classifies, and makes drawings for the 
