698 



ARTHROPODA 



considering the tubules as renal, the rectum as a bladder, and the opening as 

 an excretory pore; but this term must be kept for morphological reasons. 

 Further, he states that this excretory matter is only expelled during moulting, 

 collecting at other times in the rectum. The anus is a slit-like aperture, 

 guarded by two lateral semicircular chitinous plates. 



The male reproductive organs consist of a thin, transparent tubule — the 

 testes — ending at either end in a vas deferens, which, after coiling upon itself, 

 enters a lobulated structure — the white gland. The ejaculatory duct ends 

 in the chitinous penis. The female reproductive organs consist of a single 

 ovary, which lies across the abdomen, just behind the central alimentary sac. 

 This ends in two coiled oviducts, which open into a large spermatheca with 

 thick walls, and from which a duct leads to the genital opening. 



The tick breathes by a means of a system of tubes, lined by a spiral thread of 

 chitin. These tubes are called tracheae, and radiate, from the opening on 

 the stigma called the ' spiracle,' all over the body. The circulatory system 



Fig. 315. — A Tick LAYING Eggs. legged larva, without sexual 



present, and the little larva, becoming parasitic on some animal, sucks 

 its blood, drops off and moults, giving rise to the nympha. The 

 nympha has eight legs and a pair of large stigmata," but is without 

 reproductive openings or organs. The nymphse now become para- 

 sitic, and feed, after which they drop off, moult, and become males 

 or females with fully-developed generative organs. 



The adults now become parasitic and moult, and the young 

 female, fixing itself to the host, grows considerably, but rarely 

 changes her place ; while the male, remaining small, wanders about 

 looking for the female. 



The life-history and the habits of the different divisions of the 

 IxodidcB are so various that they will be described under their 

 separate heads. One example may, however, be mentioned here 

 — viz., Margaropus decolor atus — whose life-history has been studied 

 by Lounsbury. In this species the female, dropping off the host, 

 completes oviposition in a time varying, according to the temperature 

 of the air, from five days to four weeks, while the incubation of the 



consists of a median heart and dis- 

 tributing vessels. The fat body is 

 well marked. 



There are a number of dermal 

 glands, a coxal gland in the second 

 coxal joints and opening on the first 

 coxal joints by a minute pore, and 

 a cephalic gland in the head. 



Life-History. — While on the 

 host sucking blood, the male 

 and female parasites copulate, 

 and the latter, growing to a 

 large size, drops to the ground 

 and lays a number of eggs. 

 The egg consists of a shell with 

 an inner membrane, enclosing 

 food-yolk and embryo, which 

 eventually hatches as a six- 



{ After Sambon.) 



organs or stigmata. The 

 digestive organs are, however, 



