OF RESPIRATION. 395 



and by its compression again rejected : and by the rejection of the 

 water it is that these larvae move. 



Hair-shaped gills, which are situated upon the thorax, appear but 

 rarely to move independently ; in the majority of cases it is by means 

 of the motion of the entire animal, which is effected by the serpentining 

 abdomen, that these gills come in contact with fresh water. It is in 

 this manner that the pupa of Chironomus swims, and its whole motion 

 is consequently a respiratory motion, for these pupa take no nutri- 

 ment. A variation from this is the serpentine motion of the anterior 

 portion of the body when the animal has attached itself by its tail. 

 This motion also, which Nitzsch * observed in the pupa of Chironomus 

 plumosus, is a mere respiratory motion. Lastly, if the pupa dwells in 

 an open case, the entire bunch of gills moves either within it or on 

 its exterior : thus the pupa of Simulia appears to breathe. Whereas 

 the contact of fresh water with the bunch of gills, which in the larvae 

 of Phryganea are situated within the case, is effected by the motion of 

 the entire insect, in which fresh water is received anteriorly within the 

 cylindrical cavity, and, when expired, is again rejected by the posterior 

 aperture. 



232. 



The question now arises, how do the insects breathe which dwell 

 within the internal cavities of other animals whither little or no 

 atmospheric air can reach ? 



To answer this question, we must first illustrate the cases in which 

 insects are found in the interior of other animals. All these cases 

 refer to two chief differences, for either these insects live in cavities to 

 which atmospheric air can easily and does actually reach, and in which 

 case their respiration has nothing problematical and wonderful ; or else 

 they live in cavities which are thoroughly closed from the admission of 

 any air. The first case is found in the instance of the larvse of the 

 (Estri. These dwell either in the cavities of the nose or stomach, or 

 beneath the skin, in tumours in horses and the ruminantia. The air 

 can reach all these cavities, which also contain atmospheric air, and 

 indeed those larvse which live in tumours constantly protrude their anal 

 end, where the two spiracles are placed, out of the tumour, and thus 



Comment, de respirat. Animalium, p. 40. 



