290 



COMPARATIVE ANATOMY. 



form tufts, or lamellce, which beset the ahdomen iu the Ephemerida 

 and Perhda (Fig. 151, A), or even form a tuft on the thorax (Perhda). 

 Vague dermal respiration is here localised in definite organs. There is 

 a larger surface in the tufted form, but this is compensated for, in the 

 lamellar form, by the movements of the lamellae, and the consequent 



increase of rapidity 

 -^ in exchanging the 



Avater. When tra- 

 cheal branches are 

 developed iu the hind 

 gut, this region be- 

 comes respiratory in 

 function. Respiration 

 seems to be partly 

 effected in the same 

 region in the larv« 

 of the Ephemerida 

 and Perlida, although 

 there are no special 

 organs developed ; for 

 they have been ob- 

 served to take water 

 into the hind - gut. 

 This function is more 

 evident when the sur- 

 face is increased in 

 extent, as it is in the 

 larvae of the Libellu- 

 lida3, by the develop- 

 ment of a large 

 number of lamel]a3, 

 arranged in longitu- 

 dinal rows. Two 

 longitudinal trunks 

 (Fig. 151, B a) give 

 off branches at their 

 hinder end (c) to the 

 hind-gut, and form a close plexus of trachete in its lamellfe. These 

 internal tracheal gills are constantly bathed with water, owing to 

 the movements of a valvular arrangement at the anus. In these 

 forms therefore the hind-gut functions as a respiratory organ, just 

 as it does in many other divisions. 



Palmen, J. A., Zur Morphologie des Tracbeensystoms. Helsingfors, 1877. 



Fig. 151. A Hiuder portion of the body of the larva 

 of Ephemera vulgata. a Longitudinal tracheal 

 trunks, b Enteric canal, c Tracheal gills, d Feathered 

 appendage to the tail. B Larva of j3Sschna grandis, 

 a Superior longitudinal tracheal trunks, h Their an- 

 terior end. c Posterior portion, branching on the 

 hind-gut. o Eyes. The middle figure represents the 

 enteric canal of the same larva, seen from the side. 

 d Inferior lateral tracheal trunk, e Communication 

 with the upper trunk, a b c as iu B (after Suckow). 



§ 225. 



Among the Arachnida the tracheal system of the Galeodea most 

 nearly resembles that of the Insecta, the separate trachege being 



