148 Beviews. [Jan., 



in ■ the Echinorhynchus proteus, a species known to inhabit the trout. 

 Leuchart obtained the ova of this species, and having introduced them 

 into some water containing the water-flea (Gammarus Pulex), he found 

 they were readily swallowed by these animals. In a few days the 

 young embryoes were hatched, and found boring their way through the 

 intestinal walls into the general cavity of the body. Here they passed 

 through changes which required only about a week to complete their 

 perfect development in the intestine of their ultimate host. 



The Cestoda, of which the common tape-worm may be taken as 

 the type, are the most highly-developed forms of Helminths. They 

 embrace the various forms of cystic worms of older writers, which are 

 now known to be but larval stages in the growth of the perfect worms. 

 Within the last few years, the life-history of these creatures has 

 been thoroughly well made out, both by observation and experiment. 

 These worms pass but a short period of their existence out of the 

 bodies of their host ; but in all cases they appear in various stages of 

 their growth to occupy at least two animals of different species. The 

 tape-worms affecting man, dogs, and cats, have been most intimately 

 studied. During growth, they present the following phases of de- 

 velopment : — ■ 



1. The egg. — This is developed in the "joints," or "proglot- 

 tides," as they are called, of the mature animal. These pass away 

 from the host, and the eggs escape. In this state they pass into 

 water, or on to soil or plants, which enter the stomach and intestines 

 •of another animal. The egg appears to be favoured in its develop- 

 ment by the gastric juice of the animal which has swallowed, and 

 gives rise to the next stage. 



2. The six-hooked embryo. — Round in form, it has the hooks placed 

 in such a way as to enable it to pass easily through the walls of the 

 intestines, into the circuit of the blood, when, according to its peculiar 

 nature, it is conveyed to the liver, the brain, or the muscles of the 

 swallowing animal. Having obtained a resting-place, it is now de- 

 veloped into a cystic worm — the Coenurus cerebralis of the sheep, the 

 Cysticercus cellvlosce of the pig, or should it become abortive, the 

 hydatid of the pathologist. 



3. The cyst contains in its interior the " scolex," or " head," of the 

 perfected worm. Should this head be now swallowed by a second 

 animal, it seizes hold of the mucous membrane of the intestines, 

 and in the course of a few days becomes developed into the 

 " colonial," or tape-worm, condition, which constitutes — ■ 



4. The perfected worm, or " strobila," the perfected joints of 

 which are the proglottides, which once more produce the eggs. 



Such is the life-history of these creatures, which have been more 

 or less clearly made out in above 200 species of them. The interest 

 of this group of animals culminates in the fact that about ten species, 

 either in their cystic or perfect stages, affect the human being. 

 In their cystic stages they are more dangerous to the human being 

 than in their perfect stage. In the former they inhabit organs, as the 

 brain, the liver, and the kidneys, from whence they cannot be easily 

 expelled, whereas in the latter, they occupy the free surface of the 



