i8o 



SCIENTIFIC NEWS. 



[Aug. 24, 1888. 



invertebrate class, the brain reappears, but now in a 

 different form. In place of a localized organ, situated in 

 the head, we find it broken up, so to speak, into a number 

 of ganglia, or miniature brains, placed in different parts 

 of the body, but communicating with one another by a 

 double chain of nerves, which may or may not be 

 analogous to the spinal cord possessed by higher forms 

 of life. This structure is still more strongly marked in 

 the case of the Insects, with which we have now more 

 particularly to deal ; and in them the brain may be de- 

 fined as divided into eight, nine, ten, or more portions, 

 lying in a chain extending from the head to the extremity 

 of the abdomen, and connected with one another in the 

 manner above described. 



Now this distribution of the nerve-centre into different 

 regions of the frame leads to one most important result, 

 for it restricts, and restricts very greatly, the functions of 

 that particular ganglion which for our present purpose 

 it will be convenient to term the brain, although it is in 

 reality but a small portion of that organ. In all the 

 higher animals the brain is, of course, the ultimate ter- 

 minus of every nerve in the body, the seat of all sensa- 

 tion, intelligence, and volition, and the centre of that 

 nervous activity which enables the vital functions to be 

 maintained. Pain, in whatever part of the system in- 

 flicted, is felt by the brain ; motor stimulus, of whatever 

 muscle or muscles, proceeds from the brain. And it is 

 also the recipient of those impressions which are due to 

 the sensory organs, and which are conveyed to it by 

 special nerves, modified in character to suit their special 

 purpose. Thus its functions are many and complex, and 

 it becomes, as it were, the one great director and com- 

 mander-in-chief of the whole physical and mental organi- 

 zation. 



But in the insects it is not so. From each of the 

 ganglia in the ventral chain proceed nerves which, 

 branching and ramifying again and again, supply motor 

 force to those regions of the body in which they lie, or 

 provide for such sensory properties as may be necessary 

 for the individual species. Thus a very considerable 

 proportion of those functions which in vertebrate animals 

 are apportioned to the brain are in lower forms of life 

 dissevered from the cephalic ganglion, which may be 

 taken as representing that organ, and transferred to such 

 nerve-centre as may be nearest to the region or the 

 members in need of supply. Each ganglion, in fact, is a 

 kind of subordinate or deputy brain, a seat of motor and 

 sensory power for the service of a certain portion of the 

 body. And so the head-brain, or principal ganglion, is 

 set almost wholly free for the reception of impressions 

 conveyed to it by the sense-organs, and for the transmis- 

 sion to the secondary nerve-centres of impulses conse- 

 quent upon those impressions. At the same time, it is 

 probably affected, although not in any great degree, by 

 sensations experienced even in the remoter regions of the 

 body, for otherwise it were hard to explain the function 

 of the double communication-cord which links all the 

 ganglia together. 



Another result follows upon the first. The functions 

 of the brain being, as we have seen, almost wholly re- 

 stricted to the reception of sense-impressions and the 

 transmission of impulses to which those impressions give 

 rise, it is only natural to infer — more especially as the 

 ganglion in question is of considerable size — that such 

 impressions must be unusually keen, or at least those 

 appertaining to senses whose external receptive organs 

 are peculiarly developed. We might consider, for 



instance, that the sight of insects would be especially 

 perfect, considering the wonderful array of eyes, often in 

 two or even three forms, which are ordinarily present. 

 And such is in fact the case, as we shall subsequently see 

 when discussing the individual senses. Insects are beings 

 whose very nature, whose bright and vivid life, whose 

 matchless activity render highly developed sense-organs 

 an absolute necessity. They are primarily creatures of 

 the air, and that fact alone implies the possession of 

 perceptions unusually acute. Such we find to be the case 

 in the bat, whose highly sensitive wing-membrane en- 

 dows it with a sense of touch so marvellously perfect 

 that it can feel the presence of an object when several 

 inches away. Such we find to be the case with the birds, 

 whose eyes combine in themselves the properties of both 

 telescope and microscope, and also possess the power of 

 altering their focus with almost incredible rapidity and 

 exactness. And such, too, is the case with the insects, 

 whose sight, scent, and hearing are in many instances 

 very highly developed, while it is at least an open ques- 

 tion whether they do not possess other senses unknown 

 to ourselves, but of great and indeed inestimable value 

 in their own daily lives. 



What, for example, are the functions of the antennae ? 

 We cannot connect them with any of the five senses 

 which we generally recognise, yet their invariable 

 presence surely points them~out as organs of extreme 

 importance. They are occasionally employed as instru- 

 ments of touch, it is true, as in the case of the ants. 

 But this is the exception and not the rule ; and, on the 

 other hand, we find that those insects in which they are 

 developed to the greatest extent never employ them for 

 such purposes at all. And what can be their office ? For 

 it is not Nature's way to provide bodily members in any 

 animal without at the same time apportioning duties for 

 those members to fulfil. 



The possession by insects of additional senses, how- 

 ever, is a possibility and nothing more. However far 

 the progress of science may take us, we shall never be 

 able positively to assert either that such senses are pre- 

 sent or that they are not. And for this simple reason, 

 that, not possessing them ourselves, we cannot form any 

 idea whatever of what they may be in others. One 

 blind from his birth could call up no idea of colour, 

 neither could its character be explained to him. A man 

 born without nerves of taste could never be brought to 

 understand the nature of flavour. And in the same way 

 we can form no notion of any sense which is not a de- 

 velopment of one or more of those which we ourselves 

 possess. Thus, in discussing the presence in insects of 

 an additional sense or senses we are passing the bounds 

 of science altogether, and entering upon the regions of 

 pure speculation ; and to bring the question into scientific 

 limits is from its very nature — or perhaps it would be 

 more correct to say from our very nature — impossible. 

 We must, therefore, confine our investigation to those 

 five senses of which alone we can take any cognisance ; 

 and these, as developed in insects, we will discuss in turn 

 in subsequent papers. 



Sulphur as a Remedy for Locusts. — An interesting 

 fact in connection with the late inroad of locusts in 

 Algeria, is that one vine has escaped alone in the midst 

 of a vineyard where otherwise not a leaf has remained 

 undevoured. A few days before the arrival of the swarm 

 this vine had been well dusted over with sulphur as a 

 cure for mildew. 



