312 METAMORPHOSIS. 



the worm takes place so long as it remains in the Cyclops, but, if the Cy- 

 clops is now swallowed by a Perch, the worm undergoes a further ecdysis, 

 and rapidly attains to sexual maturity. 



The observations of Fedschenko on Dracunculus medinensis 1 , which is 

 parasitic in the subcutaneous connective tissue in Man, would seem to shew 

 that it undergoes a metamorphosis very similar to that of Cucullanus. 

 There is moreover a striking resemblance between the larvae of the two 

 forms. The larvae of Dracunculus become transported into water, and then 

 make their way into the body cavity of a Cyclops by boring through 

 the soft skin between the segments on the ventral surface of the body. In 

 the body cavity the larvae undergo an ecdysis and further development. 

 But on reaching a certain stage of development, though they remain a long 

 time in the Cyclops, they grow no further. The remaining history is unknown, 

 but probably the next host is man, in which the larva conies to maturity. 

 In the adult condition only females of Dracunculus are known, and it has 

 been suggested by various writers that the apparent females are in reality 

 hermaphrodites, like Ascaris nigrovenosa, in which the male organs come 

 to maturity before the female. 



Another very remarkable human parasite belonging to the same group 

 as Dracunculus is the form known as Filaria sanguinis hominis, or Filaria 

 Bancroft!*. 



The sexual form is parasitic in warm climates in the human tissues, 

 and produces multitudes of larvse which pass into the blood, and are some- 

 times voided with the urine. The larva? in the blood do not undergo a 

 further development, and unless transported to an intermediate host die 

 before very long. Some, though as yet hardly sufficient, evidence has 

 been brought forward to shew that if the blood of an infected patient is 

 sucked by a mosquito the larvae develop further in the alimentary tract of 

 the mosquito, pass through a more or less quiescent stage, and eventually 

 grow considerably in size, and on the death of the mosquito pass into the 

 water. From the water they are probably transported directly or indirectly 

 into the human intestines, and then bore their way into the tissues in which 

 they are parasitic, and become sexually mature. 



The well-known Trichina spiralis has a life history unlike that of other 

 known Nematodes, though there can be little doubt that this form should 

 be classified in ( respect to its life history with the last-described forms. 

 The peculiarity of the life history of Trichina is that the embryos set free 

 in the alimentary canal pass through the walls into the muscular tissties and 

 there encyst ; but do not in a general way pass out from the alimentary 

 canal of one host and thence into a fresh host to encyst. It occasionally 

 however happens that this migration does take place, and the life history 

 of Trichina spiralis then becomes almost identical with that of some of the 

 forms of the third type. Trichina is parasitic in man, and in swine, and 

 also in the rat, mouse, cat, fox and other forms which feed upon them. 

 Artificially it can be introduced into various herbivorous forms (i-abbit, 

 guinea-pig, horse) and even birds. 



The sexual form inhabits the alimentary canal. The female is vivi- 

 parous, and produces myriads of embryos, which pass into the alimentary 



1 Vide Leuckart, D. men. Par., Vol. n. p. 704. 



2 Vide D. P. Mason, "On the development of Filaria sanguiuis homiuis." Journal 

 in' the Linnean Society, Vol. xiv. No. 75. 



