WORMS. 125 



shown which give a good idea of the structure of the female and the 

 smaller male (78). The young make their way through the walls of 

 the stomach of their host, and encyst themselves among its muscles : a 

 piece of a sternothyroid muscle is shown (59), taken from a man in 

 whose body it was calculated there were forty millions of encysted 

 Trichina,. 



Other Nematodes infesting man, such as Filaria sanguinis 

 liominis, are too small for exhibition. 



Plants are not free from the attacks of Nematodes, and examples 

 are shown, accompanied by an illustrating figure, of the Ear-cockle 

 gall of wheat (66) ; this gall is due to the injuries inflicted by a 

 minute Thread-worm — Tylenclms tritici. Wheat is, of course, by no 

 means the only cultivated plant that is attacked by these minute 

 worms ; the history of most has, however, still to be made out. 



Holding a somewhat uncertain position in relation to the Eound- 

 worms are the parasitic Acanthocephali (Thorn-headed Worms) (73, 

 74) and the free-swimming CJuatognatha, or Bristle- jawed Worms 

 (75, 76) ; examples of both of these groups are shown, together 

 with diagrams illustrative of their general structure. 



Annulata or Chsetopoda. — So-called because consisting of a 

 series of rings, and being provided with chagt^e or bristles ; they 

 are to be associated with the Arthropoda, under the one head 

 " Appendiculata," a better name than " Articulata," since Cuvier did 

 not include worms in his group. The creatures that are most 

 familiarly called worms are to be found in Case III. ; here are a 

 few examples of the numerous kinds of worms that are found living 

 freely in the sea, of earth and freshwater Worms, and of Leeches, 

 All these worms are distinctly characterized by the fact that they 

 consist of a number of definite rings (somites), whence they have 

 been called Annulata. The marine Worm and the Earthworm differ 

 from the Leech in that these rings are provided with chsetse or 

 bristles, of which there are a number in each bundle in the marine, 

 and a few only in the terrestrial or freshwater form : hence the 

 marine Worms are called Polyclicda and the latter Oligochmta. 



The former are divisible into two great groups. There are those 

 that are free-swimming and are able to forage for themselves, such 

 as the lovely Sea-mouse {Aphrodite acuUata) (96), the large Halla 

 parthenopeia (87), the common Nereis pelagica (104), or the exquisitely 

 coloured Ghloeia flava (100). Others live a more retired life, dwelling 

 in tubes, which they fashion for themselves ; they lead either a solitary 

 or asocial life. Here we have examples of Terebella (226), Sabellaria 



