298 Prof. H. Karsten on RhyDchoprion penetrans. 



when they wet their feet with water after the extraction of a 

 Nigua ; but this is no peculiar effect of the Nigua. 



The swelling of the inguinal glands, observed by Ulloa and 

 Jussieu, which led them to conclude that a second species existed, 

 occurred once in my own person in La Guayra. Whether this 

 phenomenon is the specific effect of a peculiar species of animal, 

 or to be referred to the same category with the similar con- 

 sequences of other slight injuries to the lymphatics of the foot, 

 which is my own opinion, must be left to the future to decide. 

 Spix and Martius also mention swellings of the inguinal glands 

 in consequence of the penetration of Niguas. 



I cannot from my own observations confirm the opinion that 

 there are two different species of Niguas, a malignant and an 

 innocuous kind, of which the latter, according to Ulloa, is of a 

 dark colour. 



The inflation of the abdomen in the Flea, when imbedded in 

 the skin, takes place very rapidly, as has been remarked by all 

 observers. Ulloa's statement that the animal enlarges to a 

 diameter of two lines in four or five days, according to the indi- 

 vidual nature of the insect and of the subject attacked by it, may 

 be regarded as nearly correct. 



The animal imbedded in the skin, usually under the toe-nails, 

 when it has become quiescent in its new dwelling-place (that is 

 to say, when it has got so far under the epidermis that its anus, 

 lying at the same level, closes the orifice formed in the epi- 

 dermis) produces scarcely any inflammation or sensation of pain, 

 unless, as already stated, the affected spot is injured or irritated 

 by pressure or friction, in which case both these symptoms 

 make their appearance, just as in a frozen limb. The increased 

 heat and softness of the skin, in consequence of the inflamma- 

 tion, attract other Niguas, and facilitate their penetration in the 

 vicinity of the first one. This is the cause of the juxtaposition 

 of several Niguas, described by various authors, and which, in- 

 deed, is not unusual — and not, as stated by all writers since the 

 time of Oviedo, the exclusion of the larvae from the eggs in the 

 wound or in the uninjured body of the mother. Even Pohl and 

 Kollar, probably misled and rendered doubtful of the correct- 

 ness of their own observations by the statements of their pre- 

 decessors, adopt this notion of Oviedo's, although they rightly 

 understood the conditions of development and the deposition of 

 the eggs. 



As is so frequently the case, the simplest and most natural 

 state of things is the last to be recognized as the true one, after 

 all sorts of by-paths have been tried (I need only refer to the 

 theories of the origin and metamorphosis of the organic cell); 

 and the same thing has occurred here. 



