October, 1913. 



KNOWLEDGE. 



393 



Powell reports the same in regard to L. baetica, L. bellargus 

 and L. iolas. An ant removed from its companion cater- 

 pillar (L. baetica) is restless and disturbed. In the case of 

 L. bellargus the ant rides on the caterpillar and caresses 

 it. Oberthur also refers to an Australian form which lives in 

 the nests of green ants. When the imago hatches out it is 

 covered with very deciduous white scales which fall like a 

 shower of confetti when it takes to wing from among its 

 quondam companions. There seems no doubt that this 

 association of ants and caterpillars will reward further 

 investigation. 



LAND CRAYFISHES OF AUSTRALIA.— Very little is 

 known of the habits of these interesting animals (species of 

 Engaeus) which have left the aquatic habitat of their race 

 and become burrowers in damp ground. The burrows are 

 sometimes near the bank of a stream, but very frequently far 

 removed from any water in the middle of the forest in some 

 damp situation. There is water at the bottom of the burrow. 

 Messrs. G. W. Smith and E. H. J. Schuster, in a recent study 

 of the species of Engaeus, call attention to the great depth of 

 the carapace, its arched roof-like shape, the reduced 

 abdomen, the small eyes, and the tendency to reduction in 

 the size of the gills. An unusually strong hairiness of the 

 mouth-parts and neighbouring regions is probably correlated 

 with the necessity of filtering the water in the burrows, which 

 is usually very muddy. There are not a few minor losses or 

 suppressions, e.g., the loss of a flagellutn on the antennule 

 and the reduction of the antennary scale, and the authors 

 suggest that the underground burrowing habit which removes 

 the crayfis hes from active competition with other aquatic 

 forms has permitted degenerative changes which have no 

 special adaptive significance. 



The young are brought into the world and tended by the 

 female parent in the same way as in the ordinary crayfish, 

 being carried about attached to the swimmerets. As the 

 animals keep to their burrows during the day, very little is 

 known as to their feeding habits. " It is probable that they 

 are mainly carnivorous in diet, as the remains of earthworms, 

 insect larvae, and probably land Crustacea have been found 



in their stomachs The evergreen beech forests in 



Western Tasmania support a very rich terrestrial fauna of 

 land amphipods (Talitrus) which swarm under the fallen • 

 beech leaves and timber, and numerous myriopods and insect 

 larvae occur as well, affording abundant food in exactly the 

 situations which Engaeus chooses for its burrows." 



SPECIFICITY. — We have repeatedly referred in these 

 Notes to the existence of minute peculiarities of structure 

 which distinguish species, sometimes more convincingly and 

 reliably than do larger and more obvious features. A fish 

 may be known by a single scale or a bird by a single feather ; 

 and the cells lining the windpipe of a horse are readily 

 distinguished from those of the dog which barks at the horse's 

 feet. All flesh is not the same flesh, and nothing is more 

 specific than the blood. On a larger scale are peculiarities of 

 structure which run through a series of related forms. A 

 good example is furnished by Mr. Edwin S. Goodrich in his 

 study of the structure of bone in fishes. Ganoid scales are of 

 two kinds, which differ fundamentally in structure and mode 

 of growth — Cosmoid and true Ganoid. The latter are again 

 divisible into Palaeoniscoid and Lepidosteoid. The Lepidos- 

 teoid scale is easily distinguishable by the presence of a 

 system of delicate tubules running through and at right angles 

 to the bony layers. The same peculiar tubules occur in the 

 skull plates and other dermal plates of all the recent and 

 extinct Lepidosteoids and Amioids that have been examined, 

 with a single possible exception (probably a primitive form). 

 The minute peculiarity is quite distinctive. Mr. Goodrich 

 has more recently discovered that the Lepidosteoid structure 

 is exhibited not by the dermal bones only, but by the whole 

 endoskeleton as well. " The skull-bones, the ribs, even the 

 vertebral centra, are all provided with the characteristic 

 tubules traversing the bony lamellae, just as in the scales. 

 It follows that, from the examination of the minutest fragment 

 of the skeleton of a living or extinct species of fish, we can 



decide whether or not it belongs to the Amioidei and 

 Lepidosteoidei, or to some other group. The histological 

 structure of the bone, may therefore be of the greatest 

 practical value for the identification of fragmentary specimens. 

 It may also prove of great importance in the interpretation of 

 phylogeny." This is a fine instance of a minute detail of 

 structure holding good as an index of relationship. 



AFRICAN ELEMENT IN FRESHWATER FAUNA 

 OF BRITISH INDIA.— At the Zoological Congress at 

 Monaco Dr. Nelson Annandale directed attention to the 

 affinity, more close in some cases than in others, which can 

 be demonstrated between the freshwater fauna of India and 

 that of Tropical Africa. In some instances this affinity also 

 extends to South or Central America. The African element 

 in the Indian fauna was also compared with what we know to 

 exist in the fauna of the Jordan system. In the latter a large 

 contingent of the fish-fauna is pure African, but many of the 

 lower aquatic invertebrates resemble African forms much less 

 closely than do the Indian representatives of the groups. An 

 explanation may be found, on the one hand, in the more 

 recent date of the geographical connection between what is 

 now the valley of the Jordan and the river-systems of Africa ; 

 and, on the other hand, in the fact that existing conditions of 

 climate and chemical composition of the water are more 

 similar in Tropical Africa and India than they are in the 

 former and Palestine. 



GALL-PRODUCTION.— Every contribution to the study 

 of galls is welcome ; for while great progress has been made 

 towards understanding them the uncertainties remain very 

 conspicuous. How far does the mechanical irritation pro- 

 duced by the parasite count as a stimulus ? Or is it wholly 

 chemical ? To what extent do bacteria and other fungi play 

 a part in stimulation ? How far is the gall that is formed in 

 response to the stimulus a quite new sort of growth ? How is 

 it that the same plant may produce several different galls in 

 response to the stimulus of not distantly related hosts ? How 

 far can it be held that the host derives benefit from the gall 

 because it thus restricts the sphere of the parasite's opera- 

 tions ? How far, on the other hand, is the plant playing into 

 the hands of its parasite by forming the gall ? 



In a recent elaborate study of Canadian galls Mr. A. 

 Cosens maintains that the gall-producing stimulus renders the 

 protoplasm of the host more active and awakens in it 

 dormant characteristics, but does not endow it with power to 

 produce entirely new structures. The idea that the gall-pro- 

 ducing stimulus must be applied directly to the cambium is 

 not true in all cases, for any actively growing tissue will 

 respond to the gall-stimulus. Moreover the effect of the 

 stimulus is operative on tissue at a considerable distance from 

 the centre of application. There is no doubt that ferments 

 secreted by the gall-producer (Cynipidae) count for much. 

 They may pre-digest food for the larval gall-insect and may 

 indirectly stimulate cell- proliferation. 



PERIWINKLES AND THE TIDE.— It has been noticed 

 that periwinkles (Littorina littorea) shift their position on 

 the rocks in correspondence with the tidal changes. It has 

 even been maintained that this tendency to periodic move- 

 ment is so engrained in the periwinkle's constitution that it 

 takes place apart from any tides. Recent experiments by 

 Haseman do not confirm the last statement. It seems, more- 

 over, that the oscillatory movements in normal conditions are 

 not exhibited by periwinkles on horizontal flat surfaces 

 between tide-marks or when they are below the low-tide mark. 

 What seems to remain secure is that periwinkles on the 

 vertical surfaces of rocks between tide-marks exhibit up and 

 down movements which correspond with the movements of the 

 tides. 



MORE ABOUT BLACK TERMITES.— Professor Bugnion 

 has told us something more about Eutermes inonoceros, the 

 Black Termite of Ceylon. In their nocturnal excursions to 

 the trees — some of which were fifteen to twenty yards distant 

 — they usually managed to keep to the same paths. As they are 

 blind, they must feel or smell their way. Minute black specks 



