HALF-AN-HOUR AT THE MICROSCOPE. 87 



Centipede (PI. I., Figs. 3-10). — Aberrant forms of life — "con- 

 necting links"— have always a special interest to the naturalist. 

 Amongst such are the Myriapoda; these serve to connect Worms 

 with Insects, and Crustacea with Arachnida. A diagram may 

 express these relations in the clearest way, thus : — 



Annelida 



Crustacea — Myriapoda — Arachnida 



I % 



Insecta 



As is well said by Van der Hoeven — "There is in the entire 

 Animal kingdom a net, everywhere connected, and every attempt 

 to arrange animals in a single ascending series must necessarily 

 fail of success." {Handbook of Zoology^ Vol. I., p. 289.) 



Myriapods, in the first period of their life, have fewer rings, and 

 only three pairs of feet, as with all true insects. As they grow new 

 rings arise, and the number of feet is augmented. In this respect 

 also they resemble ringed worms, whilst in the metamorphoses of 

 Insects, the homologous parts, rings, segments, are not multiplied, 

 but are developed unequally, or are united, to form the different 

 divisions of the body in the perfect insect. The number, also, of 

 simple eyes increases during the development of myriapods. 

 The changes needed to convert an annelid into a myriapod, are 

 elegantly set forth by Rymer Jones in his outlines. His remarks 

 are too extended to be given here, but in brief the process consists 

 in — I St, Conversion of external branchiae into internal respiratory 

 organs (tracheae) ; 2nd, Strengthening the soft integumental organs 

 by chitinous material, the simple setae for progression to be modi- 

 fied into jointed limbs; and 3rd, Concentration of the nervous 

 system (ed. 1861, p. 280). 



Head of Gnat (PL II., Upper part).— The Q.MJ., 1855, p. 97, 

 has a remarkable paper by C. Johnston "On the auditory apparatus 

 of the Mosquito "—a creature which differs but slightly in the main 

 from our common English Gnat, Culex pipieiis. The habits of the 

 creature in a state of nature, experiments on the actions of sounds, 

 and anatomical structure, all lead the author to consider that the 

 greatly dilated basal joint in the male is the seat of the sense 

 named. I must refer our members to the original paper for details. 



