MARINE AQUARIUM PROCEDURES AND TECHNIQUES 



63 



so as to avoid the formation of hanging 

 drops, since this last-mentioned system, 

 while it rarely dries up, also cannot be 

 put back into priming action as readily 

 as the preceding system. 



We have come to the point where we 

 prefer to use the first type of capillary 

 system, which dries up frequently and can 

 be put back into priming action easily, in 

 order to create "tides" in small glass tanks. 

 This arrangement has enabled us to suc- 

 ceed with breedings which would have 

 been difficult to achieve under other condi- 

 tions. When the feeding of the tank "in 

 the tidal way" in this manner is of too 

 large a volume to have the tank emptied 

 by a capillary siphon, we have been using 

 a complex system in which the capillary 

 siphon primes one or more simple siphons. 

 This type of apparatus is rather difficult 

 to build — if not to conceive — but once it 

 has been completed, it is able to operate for 

 a very long time without any surveillance. 

 The simple capillary siphon, for tides, 

 must have a very large inlet so as to dry 

 up abruptly at the end of the operation, 

 when the air is swallowed up into the tube, 

 owing to the lowering of the water level in 

 the upper tank. 



Utilization of the "tides" 



It must be mentioned at the outset that 

 these artificial "tides" are only very dis- 

 tant relatives of the true tides which, from 

 the biological point of view, are rather 

 complex phenomena (currents and inver- 

 sion of currents, change from an agitated 

 to a calm phase, variations of the tur- 

 bidity of the water, of its temperature, salt 

 contents, luminosity, etc.) . 



The use of capillary siphons to create 

 "tides" is not limited to the breeding of 

 animals which one wants to flush out pe- 

 riodically. We shall now^ briefly review 

 the uses to which we have put them, but 

 it is possible to think of many other ap- 

 plications : 



1. It is not always easy to breed small 

 animals wlien it is desired to confine them 

 within a restricted area for "boarders" 

 (temporary occupants) which, at the same 

 time, require very frequent changes of 

 water. Into a "tidal" tank, tubes that are 

 open at both ends may be placed verti- 

 cally. As the water level is variable — 

 from the bottom of the tube to its upper 

 end — the volume of the water that passes 

 into that tube during any given period is 

 proportionate to the number of tides that 

 have taken place during the same period. 

 If it is desired to breed animals in these 

 tubes, it is sufficient to block the ends by 

 a nylon screen. In that way, the animals 

 can be isolated easily, they are able to have 

 enough water, and the breeding is limited 

 to a very small area. In practice, the 

 breeding tubes are assembled into bundles, 

 and only their lower end is immersed into 

 the "tidal" tank (fig. 7). 



2. For breeding of animals within the 

 upper limit of the tides (fig. 8), a tank 

 (A) receives water from the exhausting 

 device through a large pipe which 

 descends to the bottom of the tank. A bed 

 of gravel has been placed on that bottom ; 

 it is covered with a screen and with sand — 

 an arrangement that is similar to the sand 

 tank which we shall discuss later. The 

 breeding tank proper (B) has been placed 

 on the bottom of the sand layer; this tank 

 consists of a glass cylinder which is closed, 

 at its upper end, by a removable sheet of 

 glass (F). Pebbles collected on the sea- 

 shore have been placed inside the cylinder 

 on a layer of sand the thickness of which 

 varies but must be such that its level is 

 very considerably lower than level 1. 



The level of the water in tank A varies 

 between 1 and 2, because of the siphon C. 

 The water ascends and descends in cylin- 

 der B ; it wets part of the pebbles which, 

 therefore, retain a high humidity. The 

 water in cylinder B acts amidst the peb- 

 bles like a piston, in such a manner that 



