734 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



SO named by BruUe, and called the cardo by Kirby and Spence. 

 Oligotoma Saundersii is taken as the starting point, and its sub- 

 maxillary described as being a small transverse piece slightly grooved 

 on its inner surface. CEdipoda cinerascens has the same part provided 

 with several deep articular cavities. In Decticus the organ is still 

 more modified. In Gryllus domesticus it is strongly, and in Phasma 

 japetus feebly articulated. In Mantis religiosa it is developed in a 

 vertical direction, and has the appearance of some maxillae. In 

 HydropTiilus piceus the different portions of the organ are profoundly 

 modified. The author considers that the descriptions which he gives 

 are sufficient to show the interest which attaches to the morphological 

 study of the submaxillary, and the changes undergone by a part which 

 has been too often misunderstood, but whose correct interpretation 

 is necessary in a comparative study of the appendages of the 

 Arthropoda. 



Structure and Function of Legs of Insects.* — F. Dahl ascribes 

 our ignorance of the structure and functions of insects' legs to the 

 fact that on the one hand most entomological works are of a purely 

 systematic character, and that, on the other, anatomists have chiefly 

 busied themselves with the axial parts only ; in fact, Strauss- 

 Durckheim, Newport, Burmeister, and Graber are the only authors 

 to whom Dahl makes reference in his introduction. 



The constancy of the number of six is probably to be explained 

 as being in relation to the function of the legs as climbing organs ; 

 one leg will almost always be perpendicular to the plane when the 

 animal is moving up a vertical surface ; and on the other hand we 

 know that three is the smallest number with which stable equilibrium 

 is possible ; an insect must therefore have twice this number, and the 

 great numerical superiority of the class may be associated with this 

 mechanical advantage. This theory is not weakened but rather 

 supported by the fact that the anterior pair of legs is rudimentary 

 in many butterflies, for these are almost exclusively flying animals. 



The author describes in some detail the arrangements of the 

 muscles of the legs ; the nerve-cord supplying them is pretty stout, 

 and the large number of filaments sent to the joints of the tarsus 

 lead to the supposition that these have a tactile function ; the nerve- 

 fibres are seen to enlarge into thick spindle-shaped ganglia. There 

 are two tracheal trunks. 



The prime function of the legs is locomotor, and insects move 

 through gaseous, fluid, and solid media. The last is seen in fossorial 

 forms, of which Gryllotalpa may be taken as the type ; here some of 

 the joints are flattened out and provided with teeth, and the muscles 

 are well developed. In some cases legs of a fossorial type are 

 possessed by insects which move on the ground, but the larvse of 

 which are subterranean in habitat. The water-beetles and aquatic 

 Rhynchota have the legs converted into swimming organs ; they are 

 widened out into plates and provided at the sides with movable hairs, 

 which are directed slightly backwards. The median pair of legs in 

 Corisa is provided with two very long hooks, the function of which is 



* Arcliiv f. Naturg., 1. (1884) pp. 146-93 (2 pis.). 



