TKANSMIGBATIONS AND METAMOKPHOSES. 251 



nematode of the rat ; the female is 2"5 millimetres in 

 length, and the male "17 millimetres, and it lives in the 

 uterus of its female. Five males are occasionally found 

 in one female. This observation made by Leuckart has 

 been confirmed by Biitschli. The male has its digestive 

 tube incomplete ; its female feeds for it. 



The bat of the high mountains of Bavaria, known 

 under the name of Vespertilio mystacinus, harbours a 

 nematode, the Rictularia, plagiostoma, the same which is 

 found in Egypt in the hedgehog (Erinaceus auritus). 

 The bat on the banks of the Bhine has not this 

 remarkable worm. We must therefore conclude that 

 the bat of Bavaria finds and eats the same insect as the 

 hedgehog in Egypt, and that this insect does not live on 

 the banks of the Bhine. We have never met with this 

 nematode in the myBtacines of Belgium, and yet we have 

 opened them by hundreds. 



A bird found in Florida, the Anhinga, has in its 

 brain a nematode whose presence in that organ is not 

 accidental. 



The Echinorhynchi form a very remakable group of 

 parasites. They migrate from one host to another ; but 

 the vehicle by which the greater part of them is con- 

 veyed is not known. We represent in Fig. 72 a species 

 which is very common in the intestine of the sprat. 



It is known that these worms migrate when young, 

 and undergo metamorphoses when they change their 

 host. The Asellus aquaticus of fresh water, harbours 

 besides other worms, the Echinorhynchus hceruca; the 

 Gammarus pulex, another fresh-water crustacean, lodges 

 the larva of the Echinorhynchus proteus (Fig. 72). We 

 commonly find this beautiful species of the Echino- 



