306 Prof. H. Karsten on Rhynchoprion penetrans. 



It is remarkable that, during the parasitic existence of the 

 female, its trachese entirely lose their peculiar spiral structure, 

 and acquire considerably thickened walls; these changes take 

 place first in the finer ramifications, and subsequently in the 

 branches and stems, which, before the thickening becomes per- 

 fectly uniform, sometimes acquire a porous aspect. The cause 

 of this extraordinary phenomenon, connected as it is with para- 

 sitic existence, is probably to be sought partly in the altered 

 mode of nourishment and partly in the residence of the animal 

 within the tissue, more or less permeated by fluids, of the living 

 organism which furnishes the nutriment. On the one hand, by 

 continual sucking, an extraordinary amount of fluid is taken 

 up (if we may judge from the constant issue of lymph after 

 unsuccessful operations, as already mentioned) ; and on the 

 other hand, the evaporating surface of the animal is reduced to 

 a minimum. The greater part of the integument of the para- 

 site is entirely prevented from taking part in transpiration; 

 those segments which contain the last stigmata transpire more or 

 less incompletely, as even these segments have only a very small 

 part directly exposed to the atmosphere. Perhaps this may be 

 the cause of the considerable thickening both of the true air- 

 passages themselves and also of these last abdominal segments; 

 whilst the anterior and larger segments of the abdomen lose 

 their chitinous plates by stretching them into very delicate 

 membranes. 



As I found no air in these altered and thickened trachea?, it 

 would almost appear as if these air-canals had suspended their 

 normal functions during the parasitism of the insect — as if the 

 tissue forming them vegetated on in an altered form indepen- 

 dently of the developmental laws otherwise governing them, 

 whilst the ovicells assimilated the unaltered lymph of the nutritive 

 organism, which is continually brought to them by means of the 

 sucking-apparatus acting by capillarity and adhesion. For the 

 entire tractus intestiualis appears, as in chrysalides, to be sub- 

 jected to a retrogressive metamoi-phosis ; and the life of the animal 

 during its parasitism, like that of many other endoparasites, seems 

 to become purely vegetative. 



Do the aeriferous trachece change their function in such a 

 manner, during the residence of the animal in the tissues of the 

 skin, that they are filled with lymph, instead of air, through the 

 stigmata, and in consequence become thickened ? This hypo- 

 thesis, improbable enough in itself, is contradicted by the cir- 

 cumstances, that the last stigma of each side, which opens into 

 the cloaca, is always freely exposed to the air, and that the stig- 

 mata concealed by the dermal tissues are not in the corium, but 

 applied to the dry, horny epidermis (at least, the three pairs of 



