SEVENTEENTH ANNUAL EEPORT. 



399 



molt. Specimens were taken which showed the tick nearly ready to emerge from 

 the old skin, through which they could be seen. The larva (Megnin) is six-footed, 

 possesses no sexual organs, and wants the large single stigmata found in later stages. 

 I think it breathes through the six stigmata-like dots I have observed on the sides 

 just behind each pair of limbs, but I have not yet made all the sections and exami- 

 nations necessary to sustain this point. The digestive and urinary tracts and cloacal 

 pore are present, and apparently vary little in the successive stages. 



The next, or nymphal, stage, as seen through the skin of the larva, has added a pair 

 of limbs behind the others and a pair of large stigmata behind them. The additional 

 legs lie along the sides in a loop with its convexity directed caudally. The contents 

 of the three front pairs of legs have withdrawn until only their white tips remain in 

 the testa about to be molted. The head itself is withdrawn from the external skin 

 and the mouth parts seem to be entirely disconnected from it. 



Molting in this stage is completed by the testa first splitting along the side in the 

 vicinity of the head, the feet being thrust out through it, and the dorsal and ventral 

 halves torn apart by the force of the limbs. Specimens of the loose valves and a tick 

 with its feet thrust through the slit near the head, which are now in the Bureau 

 collection, demonstrate this satisfactorily. 



In the change from the larval to the nymphal stage there is a complete ecdysis, 

 accompanied by the addition of new parts. The change is therefore incomparable 

 to the stage of metamorphosis in insects, and the terms larva and nymph can only be 

 used in a restricted sense as applied to these stages as being analogous, but not homol- 

 ogous, with those stages bearing the same names among the insects. The important 

 changes at this molt occur in the locomotory and respiratory organs. 



The next specimens were collected a week later, on November 29. The collection 

 contained individuals about to change from the nymphal to the adult stage, which, 

 like the others, could also be seen through the testa they were about to shed. I had 

 previously been enabled to study this stage from field collections, but the specimens 

 collected at this time were invaluable in completing the life history of the ticks as 

 learned from a single brood. 



The molting at this period is complete. The limbs and head are withdrawn a 

 little from the old testa. . The valves split along the sides as in the earlier molt. 

 The digestive and respiratory and locomotory organs undergo little if any modifica- 

 tions.^ The greatest change occurs in the reproductive organs, which have developed 

 during the nymphal stage and assume their functions immediately after theecdysis, 

 when the genital orifices appear in the new skin. Beyond this and the more 

 decided adult characters offered in conformation there seem to be no essential changes. 



The differences between the ticks destined to become either male or female during 

 their final molt is not marked. The average of the males is smaller, but a small 

 female may not be any larger than an ordinary male. In each the mouth ring and 

 mouth parts, the shield-like headpiece, the breathing pores, the limbs, and the body 

 are alike. 



After they emerge, however, the males can be quickly chosen by their smaller 

 size, by the absence of a well-defined head shield, by the extension of the shield 

 over entire back, and by the two pairs of triangular chitinous plates, situated on the 

 abdomen, behind and on each side of the anus. The female looks much as in her 

 earlier stage; the head shield is, however, larger and stronger, the lines made by the 

 muscular attachments to the body walls are stronger and deeper, and the breathing 

 pores are much enlarged. The limbs in both male and female are strong and large 

 as compared with their bodies, and fit them for retaining their place on their host 

 until they have gained a new attachment by their mouth or rostrum. The external 

 genitals which appear in the adults are very similar in each sex and occur between 

 the bases of the second pair of legs. They present little more than an opening sit- 

 uated on the median line of the belly. 



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