220 in k president's address. 



female is often totally different in appearance from the same 

 creature at the earlier period when fecundation takes place. This 

 has heen called " Pedogenesis," and an instance of it occurs in a 

 parasite which is not an Acarus. The crustacean once called 

 Praniza is parasitic, and is fecundated at that stage, but it is the 

 young of the free-living Anceus, and the eggs are laid in the latter 

 condition. A curious connection exists between the Dermaleichi 

 and another small group of Acarina, the Cheyleti ; oddly enough, 

 Van Beneden gives eruditus as the parasitic species. All the 

 Cheyleti are predatory creatures, living on small, soft-bodied Acari 

 and Insects, and are constantly searching for them. This leads the 

 free-living kinds, of which eruditus is one, into all sorts of 

 localities, and it has been described by authors who were not 

 acquainted with its inquisitive habits as a resident in very strange 

 places ; but there is one small group of the Cheyleti which probably 

 really may be called parasites ; they are Cheyletus parasitivorax, C. 

 heteropalpus, &c. These live permanently upon birds, but only to 

 devour the Analgince, by which the bird's feathers are infested. 

 Here, says Megnin, is an " auxiliary parasite," a sort of exaggerated 

 mutualist, whose parasitism consists only in ridding his host of 

 other parasites. This appears to be so, but if the Analgince be 

 really beneficial parasites the position of the Cheyletus may be con- 

 siderably modified. 



It is not only on the feathers of birds that acarine parasites 

 exist. Lamina sioptes gallinarum and Cytoleichus sarcoptoides live 

 in the air-chambers, and on the serous membranes in such numbers 

 as sometimes to kill the host, while the singular Harpirhynchus 

 nidulans is found in the follicles at the roots of the quills, and the 

 still stranger nymph of Syringophilus bipectinatus, with its tarsi 

 terminated by a whole bunch of hooks, is found inside the quills 

 themselves. There are plenty of other acarine parasites, but I will 

 only refer to one which Professor Allman discovered in such an 

 unexpected place as the nares of the seal. It is called Halarachne 

 Halichceri, and has lately been carefully studied by Dr. Kramer. 



I will now very shortly refer to a few only of the very numerous 

 interesting parasites which are not Acari, but I shall wholly omit 

 the intestinal worms, because, although these, from their life- 

 histories, are the most curious of all, yet so much has been written 

 about them of late, and so much said about them at this Society, 



