NEMATELMINTHES. 377 



oesophagus. They then grow rapidly in length, and at a second ecdysis 

 acquire a peculiar beaker-like mouth cavity approaching that of the adult. 

 They do not become encapsuled. No further development of the worm 

 takes place so long as it remains in the Cyclops, but, if the Cyclops 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 larva? of the two forms. 

 The larva; 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 comes 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 herma- 

 phrodites, 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 

 Bancrofti 2 . 



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

 produces multitudes of larvae which pass into the blood, and are sometimes 

 voided with the urine. The larvae in the blood do not undergo a further deve- 

 lopment, 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 tissues and 

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



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



2 Vide D. P. Manson, " On the development of Filaria sanguinis hominis." 

 Journal of the Linnean Society, Vol. xiv. No. 75. 



