THE INTERNAL STRUCTURE OF ANTS. 49 



The Respiratory System. The tracheae of ants are not unlike 

 those of many other insects, as shown by Janet's studies (1902) of 

 Mynuica and other genera. In all ant-larvae there are ten pairs of 

 stigmata or tracheal orifices occurring on the meso- and metathoracic 

 and first to eighth abdominal segments. These stigmata also persist in 

 the adult ant as small, round openings. According to Janet the meta- 

 thoracic pair is closed in the Alyrmicinae (Mynnica), but remains open 

 in the Camponotinae ( Formica ) and Dolichoderinae ( Tapinoina ) . Each 

 stigmatic orifice leads into a short stigmatic trunk which is furnished 

 with a very interesting valve by means of which it can be closed (Fig. 

 25). The stigmatic trunks of the thorax and gaster bifurcate in an 

 anterior and posterior direction and the two branches fuse on each side 

 of the body to form a continuous longitudinal trunk. This is very 

 large in the gaster, but much more tenuous in the thorax, where a 

 second pair of more dorsal longitudinal trunks is formed, which, in the 

 queens and males, supplies the wing muscles with air. The gastric 

 trunks dilate and contract with the so-called respiratory movements of 

 the external skeleton and in this manner the air is pumped into and 

 out of the finest ramifications of the tracheae. The gastric trunks are 

 united by ventral, transverse, anastomosing tracheae and also give off 

 segmental dorsal branches which break up into finer and finer ramifi- 

 cations to supply the various viscera. 



The Muscular System. For an account of this system in ants the 

 reader must be referred to the articles of Janet, Nassonow, Berlese and 

 Lubbock, as the subject is one of too great complexity and detail to be 

 treated within the limits of this work. Still there is an ontogenetic 

 change in the muscular system of the adult queen ants, which cannot 

 be passed over, as it is of no little ethological importance. I have often 

 observed that aged, dealated queens will float when placed in water 

 or alcohol, and that when the thorax of immersed specimens is pierced 

 with a needle, large bubbles of air escape, showing that the wing mus- 

 cles must have atrophied. Janet (1906, 190/0, 1907/7 ). has studied the 

 histological changes, which lead up to this peculiar condition in Lasiits 

 niger, and finds that the muscles, which in the virgin queen fill up most 

 of the thoracic cavity and are well-developed and beautifully striated 

 till the marriage flight occurs, are completely broken down within a few 

 weeks after deflation (Fig. 26). He maintains that this sarcolysis is 

 not due to phagocytes devouring the muscles piece-meal, but that the 

 blood corpuscles (amoebocytes) which creep in among the fibrilloe take 

 up spontaneously the dissolving muscle substances and convert these 

 within the cytoplasm into fat globules and albuminoid granules. Thus 

 the amoebocytes become adipocytes and replace the muscle fibrillae (Fig. 



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