ALTERNATE PARASITISM OF GORDIUS. 



331 



escapes into the water, where it passes the early part of its life. Fig. 66, F, represents 

 the embryo of Gorclius aquaticus greatly magnified. It will be seen how greatly it 

 differs from the adult hair-worm, having in this stage some resemblance to the Acantho- 



cephalus by its cephalic 

 armature, to the Nematoidea, 

 or thread-worms, by its ali- 

 mentary canal, and to the 

 larvse {cer carta) of the Trc- 

 motodes, or fluke- worms, in 

 the nature of its secretory 

 glands. But the hair-worm 

 differs from all these worms 

 and even Mei^mis, a hair- 

 worm much like, and easily 

 confounded with, Gordius, in 

 having a complete metamor- 

 Xjhosis after leaviug the egg. 

 When in this stage, it in- 

 cessantly protrudes and re- 

 tracts its armed head, the 

 spines being directed back- 

 ward when the head is out. 

 In the first period of larval 

 life the worm lives encysted 

 in the bodies of aquatic fly- 

 larvsB. The vessel in which 

 M. Villot put his Gordius 

 eggs also contained the lar- 

 vfB of Tanapus, Corethra, and 

 Chironomus, small gnat-like 

 flies. He found that each of 



these larvsB contained nu- 

 riG. 66.— Gordius AQUATICUS.— A, egg; B,egguTiderffoino;se'rmenta- , -.^ i«^ ^ ^-c 



tionoftheyolk; C, embryo (gastrala) with the primitive stomach an in- merous cystS WltU larvSB Ot 

 fold of the outer germinal layer of cells (ectoderm) ; D, embryo larther Qordius. He then removed 

 advanced ; E, larva, with the three circles of spines retracted within , , ' j. , , 



the oesophagus; F, the same stage greatly enlarged to shjw the in- the larvSB trom the cystS, 

 ternal orgaus; c, middle circle of spines, the head being retracted ;?«,, „|„„gjq them on the ffuat- 

 muscular !ayer(?); t, beak or proboscis; 4, intestine; z, z, embryonal ^ ® 



cells;/, excretory tube leading from gr, the secretory glands; CB, ojsnph- larva, and saw the larval 

 agus ; V, rectum; ?i, anus; Gr, the second larva, encysted io a fish— , . t n-c t,>ott 



(after Villot). H, Gordiwswnw*, end of body of male, much enlarged, "^air- worm worK Its way 



I, Gordius aquaticus, end of^body of male, much enlarged. K, Gordius into the head of the gnat- 



larva through the softer 



aquaticus, natural size. (H, I, K, drawn by J. S. Kingsley.) 



part of the integument ; during the process the spines on the head, reversing their 

 usual position, enabled the worm to retain its position and penetrate farther in. Then, 

 finding a suitable place, it came to rest and remained immovable. Then the fluids 

 bathing the parts coagulated, and formed a hard, granulated sac. This sac at first 

 closely envelops the body, then it becomes looser and longer, the worm living in the 

 anterior part, the front end of the sac being probably never closed. In this first larval 

 state, the worm is active. 



In the second larval period the young hair-worm lives motionless and encysted in the 

 mucous layer of the intestines of small fish, which prey on the gnat-larvae. A minnow, 

 for example, swallowing one of the aquatic gnat-lflrvsB, the encysted larva becomes 

 set free by the process of digestion in the stomach of the fish ; the cyst dissolving, the 

 young hair-worm itself becomes free in the intestine of its new host. Immediately it 

 begins to bore, aided by the spines around the head, into the mucous membrane lining 

 the inner wall of the intestine of the fish, and then becomes encysted, the worm itself 

 lying motionless in its new home, with its head retracted and the tail rolled in a spiral. 

 The cyst is either spherical or oval. (Fig. 66, G.) 



