752 THE MICROSCOPE. 



kind of cough ; in lambs filarian worms accumulate 

 rapidly in the air-passages and lungs, and a number of 

 animals perish annually from what is called " the lamb 

 disease." The worm represented in fig. 1 is the much- 

 dreaded Trichina spiralis. This nematode worm derives 

 its name from the circumstance that it was found spir- 

 ally encysted in the flesh of pigs. It is usually found 

 curled up in a spiral form in the middle of the large 

 muscles. Before attaining to the encysted stage, it has 

 a free existence, lives an aquatic or wandering life, and 

 hides in moist situations or in bogs. It very closely 

 resembles the filarian worm Anguillula fluviatilis (fig. 

 3) . Very many of the Anguillulidae are parasitic upon 

 water- snails, slugs, earthworms, and the larvae of in- 

 sects. They are remarkable for their tenacity of life, 

 resisting the extremes of heat and cold. 



Trichina spiralis infests man and numerous warm- 

 blooded animals the pig, dog, rabbit, rat, &c. In 

 forty-eight hours after the embryos are taken into the 

 stomach they attain to maturity. They are most active 

 little worms, in four days are full-grown, and are then 

 rapidly carried by the blood-current and deposited in 

 the muscles in almost every part of the animal body. 

 The nature of the fever produced by these terrible 

 parasites is as remarkable as it is fatal. 



Another species of filarian worm, found in Thames 

 water, is named by Von Baer Chcetogaster lymncetis 

 (fig. 2), from its having been first observed crawling 

 over water-snails, Lymnaeus, and Planorbis. These 

 worms are often found in specimens of Thames water, 

 and they attract attention from their rapid, cater- 

 pillar-like motion over the body of their host. Chce- 

 togaster lymnceus is a very translucent, thread-like, 

 whitish worm. The oral aperture is capable of a con- 

 siderable amount of distension, like that of the eel. 

 Its action is very rapid, and its body so transparent, 

 that it is a difficult matter to trace the nervous system. 

 It is affirmed by some observers that it feeds upon 

 cercariae. I cannot, however, confirm this observation, 

 but I have seen its stomach filled with diatoms. 

 Chsetogaster are found in the body of the common 



