PARASITES FREE WHILE YOUNG. 143 



sheep market, a servant found one morning three 

 attached to the skin of his breast. Delegorgue speaks 

 of some very small reddish ticks in Africa, which cover 

 the clothes by thousands, and produce distressing itch- 

 ing. Others are found in different parts of the globe, 

 and twenty-four species have been described. Several 

 new American Ixodes have been noticed lately by Mr. 

 Packard on the stag, the monax marmot, the Lepus 

 palustris, &c. These arachnida live at first in freedom in 

 the bushes, but after fecundation the female attacks the 

 first mammal which she' finds in her way, and establishes 

 herself upon it ; dogs become infested with it by running 

 in and out among the brushwood. 



The Argas reflexus lives on pigeons, and is allied to 

 the Ixodes. E. Buchholz has lately studied many 

 new acaridas found on different birds. 



If the forms are not so varied among the isopods as 

 elsewhere, many among them present nevertheless the 

 most extraordinary appearance, the most unexpected eon- 

 tour. Most of the parasitic isopods instal themselves 

 in the thoracic cavity under the carapace of a neighbour, 

 and make themselves contented in the small space which 

 remains to them. After having disposed of their 

 luggage, they arrange themselves scrupulously according 

 to the extent of the lodging which they occupy, and, 

 rather than interfere with the branchiae, they raise up 

 the walls of the cephalothorax, thus forming a sort of 

 tumour which betrays the presence of the intruder. 

 Others are found which are not contented with a natural 

 cavity ; they raise the scale of the skin of a fish, per- 

 forate or hollow out the true skin, or even pierce through 

 the walls of the abdomen, in order to establish themselves 

 8 



