658 



ZOOLOGY 



SECT 



Different kinds of Pycnogonicls occur at various depths from between tidal 

 limits to considerable depths in the ocean. The larvae of the species of one 

 genus are internal parasites in certain hydroid Zoophytes. 



THE LlNGUATULIDA OB PENTASTOMIDA. 



The Linguatulida (Fig. 569) are parasitic animals, which, when super- 

 ficially examined, present little appearance of affinity with the Arthropoda. 

 The body is completely worm-like, not divided into regions, and presenting 

 only a superficial annulation, which in no way corresponds with division of 

 the body into segments. The sole representatives of limbs are four hooks 

 (hk.) at the sides of the mouth. The muscular fibres are striated. The 

 alimentary canal is simple and straight, and Malpighian tubes are absent. 



fifv 



FIG. 569. Fentastomum taenioides, 



young female. 'an. anus ; gang, ganglion ; 

 hk. hooks ; mo. mouth ; ces. oesophagus ; 

 ov. ovary ; ovd. oviduct ; rec. sem. re- 

 ceptaculum seminis ; sex. ap. sexual 

 aperture ; stom. stomach ; ut. uterus. 

 (After Leuckart.) 



FIG. 570. Macrobiotus hufelandi. 



I IV, appendages ; bucc.buccal cavity ; 

 gld. accessory gland ; mal. Malpighian 

 tube ; ov. ovary ; rect. rectum ; sali. 

 salivary glands ; stom. stomach ; sty I. 

 teeth. (From Hertwig's Lehrbuch, 

 after Greef and Plate.) 



Heart and organs of respiration are wanting. The nervous system is greatly 

 reduced. A narrow nerve-collar surrounds the oesophagus, presenting no 

 brain- enlargement, and connected behind with a single ventral nerve-mass. 

 Organs of special sense are absent. 



Some species of Pentastomum are in the adult condition parasites in the 

 lungs of snakes. One species (Pentastomum tcenioides) inhabits certain 

 cavities the frontal sinuses and maxillary antra connected with the nasal 

 chambers in the Dog and Wolf. Its embryos, escaping and falling on grass 

 and other herbage, which form the food of Hares and Rabbits, are taken up 

 by these animals, and perforating the wall of the alimentary canal, by means 

 of a boring apparatus composed of several chitinous pieces, lodge themselves 

 in the liver, where they become encysted and undergo a metamorphosis. 



