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SYSTEMATIC ZOOLOGY 



the body, the anus at the posterior. There are two chitinous 

 hooks on each side of the mouth, but no appendages. The 

 sexes are separate ; the male genital opening is just posterior 

 to the mouth, the female is near the anus. In one species, 

 Pentastomitm tcenioides (Fig. 182), the female is about eight 

 centimeters long, the male only two centimeters. 



The life history of these parasites is somewhat complicated, 

 and two hosts are necessary for their development. The embryos 

 pass from the nasal chambers of the hosts mentioned above, 

 and getting on grass or other plants, are eaten by such animals 



as hares and rabbits, in which they 

 develop into larvae, provided with two 

 pairs of appendages. These larvae 

 occur generally in the liver ; one species 

 has been found in the liver of negroes 

 in Africa. When the host of these 

 larvae is eaten by carnivorous animals, 

 they develop into the mature state in 

 the nasal chamber. For some time 

 these animals were classified with the 

 worms, but the presence of the append- 

 ages in the larva is considered as 

 relating them to the Arachnida. 



Supplementary Order Pycnogonida 



The Pycnogonida (Gr. ttvicvos, thick, 

 and yow, knee), sometimes called the 

 sea spiders (Fig. 183), are exclusively 

 marine, some living amongst seaweeds 

 and hydroids along the shore, others at 

 great depths ; some are only a milli- 

 meter in diameter, some deep-sea 

 species are over sixty centimeters in 



an. sex cp 



FlG. 182. Pentastotnum tcenioides. 

 Young female; highly magnified. 

 an, amis; gang, ganglion; kk, 

 1 ks; mo, mouth; rns, oesoph- 

 agus ; ov, ovary ; ovd, oviduct ; 

 rec.sem, receptaculum seminis; 

 sex.ap, sexual aperture; stom, 

 stomach; ut, uterus. (After 

 Leuckart, from Parker and 

 Haswell's Text-book.) 



diameter. The body, which is always 

 small, consists of a cephalothorax and abdomen. The anterior 

 portion of the cephalothorax is unsegmented ; the posterior part 

 consists of three segments, to the last of which the very rudi- 

 mentary, unsegmented abdomen is attached. The anterior end 



