OF WASHINGTON. 279 



state a flat, nearly circular form and is in many parts, as the legs, 

 the capitulum with the appendages, and in some parts of the body, 

 semi-transparent. The specific characteristics of this stage are, 

 first, the presence of only six legs, the fourth (posterior) pair 

 being absent ; second, the absence of the generative system and, 

 externally, the orifices of the sexual organs ; third, the absence 

 of the respiratory organs, and here this first stage of a higher de 

 veloped form shows a peculiar relationship with the inferior 

 group of Acari the Atracheata. The six legs are comparatively 

 long and the joints thicker and swollen. The empty stomach 

 can be recognized through the hyaline integument as a white, 

 somewhat cloudy spot, while the caecal intestines often show 

 traces of black faecal matter, and thus give to the body a figured 

 aspect. The anterior part of the dorsal surface is covered more 

 or less widely by a somewhat darker colored shield which is gen 

 erally very conspicuous and varies in the different species but 

 very little in length and width ; when the eyes are present in the 

 adult stage, they are indicated by darker spots. The mouth-parts 

 are imperfect, the plates and hooks of the maxillae and the tip of 

 the mandibles rudimentary or only indicated, but the epidermis 

 is already provided for an abnormal extension in case the animal 

 is so fortunate as to find a vertebrate host to fill itself with its 

 blood. This possibility of an immense extension is due to a 

 peculiar condition of the integument, which consists of number 

 less minute corrugations or wrinkles. These folds may be 

 smoothened out by a pressure from within and afford thus a 

 greater capacity of expansion, which is necessary in a parasitic 

 state of life. 



Three very small orifices may be observed : the first, close to 

 the margin, between the first and second coxae and the last; the 

 next, between the second and third coxae, and the last, behind 

 the third coxae, the two latter somewhat removed from the mar 

 gin of the body at the underside. Although these openings 

 resemble stigmata, I have been unable to observe any traces of 

 tracheae attached to them, and I presume that they may be open 

 ings of some glands (coxal glands?). 



After the first moult the Tick enters into the second or nymphal 

 stage, which is characterized, first, by the presence of the fourth 

 pair of legs. The process of this development has been going on 



