42 
Tanks No. 23 and 25. 
wonderful thing is that the crab knows its friend, and not only tries to 
put anemones on shells which are devoid of them, but actually takes 
its companions along with it, when it changes its house! Observations 
and experiments have placed this beyond all doubt, and prove this alliance 
to be one of the most remarkable known among lower animals. 
The life of the Hermit-crabs in the Aquarium is rich in varied and 
amusing scenes. The droll fights of the little troop, the way they tumble 
about, flee and follow each other up, the impudent seizures of some 
and resolute defence of the others during the common meal invariably 
excite the laughter of the spectator, who is often greatly surprised at 
the artful and calculating ways of the little creatures. 
In these habits the Hermit-crabs rank next to the true 
Crabs, .to which we w r ill now turn our attention. 
In the Hermit-crabs we noticed a retrogression 
in the rudimentary development of the tail, brought 
about by their mode of life. In the short-tailed 
Crabs (Brachyura) this retrogression has gone still 
further, but has been accompanied by an increase 
in agility. Here the large portion of the body which 
forms the tail of the lobster, is reduced to a small round or triangular 
plate which is doubled up under the stomach-region and is therefore not 
seen from above. The anterior part of the body is laterally expanded 
Fig. 63. Pisa tetrao- 
don, V 2 nat. size. 
Tank 25. 
and is mostly of a roughly triangular or square shape; the well known 
Shore-crab may serve as a type. 
To begin with we would mention the Crabs with a triangular body. 
The first point which will attract notice in these, is the curious way in 
which they are covered with all sorts of foreign substances; thus Pisa 
(Fig. 63 , tank 25) carries quite a forest of small algae and colonies 
of animals (Polyzoa and Hydroid-polypes) on its back and legs; Inaehus 
