TREMATODA. 567 



formed digestive apparatus is accurately represented in 

 Plate IV. Nos. 106 and 107, Fasciola gigantea of Cobbold, 

 which should be contrasted with the somewhat similarly- 

 racemose character of the water- vascular system. Let it be 

 expresely noted, however, that in the digestive system the 

 majority of the tubes branch out in a direction obliquely 

 downwards, whereas those of the vascular system slope 

 obliquely upwards. A further comparison of the dis- 

 position of these two systems of structure, with the 

 same systems figured and described as characteristic of 

 the Amphistome, will at once serve to demonstrate the 

 important differences which subsist between the several 

 members of the two genera, if we turn to the con- 

 sideration of the habits of Fasciola hepatica, which, 

 in so far as they relate to the excitation of the liver 

 disease in sheep, acquire the highest practical import- 

 ance. Intelligent cattle-breeders, agriculturists, and veteri- 

 narians have all along observed that the rot, as this 

 disease is commonly called, is particularly prevalent after 

 long-continued wet weather, and more especially so if 

 there have been a succession of wet seasons ; and from this 

 circumstance they have very naturally inferred that the 

 humidity of the atmosphere, coupled with a moist condi- 

 tion of the soil, forms the sole cause of the malady. Co- 

 ordinating with these facts, it has likewise been noticed that 

 the flocks grazing in low pastures and marshy districts are 

 much more liable to the invasion of this endemic disease 

 than are those pasturing on higher and drier grounds ; a 

 noteworthy exception occurring in the case of those flocks 

 feeding in the salt-water marshes of our eastern shores." 1 

 Plate IY. No. 106, Fasciola gigantea : the anterior surface 

 is exposed to display oral and ventral suckers, and the 

 dendriform digestive apparatus injected with ultramarine ; 

 No. 107, shows the dorsal aspect of the specimen and 

 the multiramose character of the water-vascular system, 

 the vessels injected with vermilion. 



One of the most remarkable of the Trematode helminths 

 is Billiarzia hcematobra of Cobbold ; Distomia hcematobium 

 of some other authors. Plate IY. No. 102. This genus 



(1) Entozoa: An Introduction to the Study of Helminthology. By T. Spencer 

 Cobbold, M.D.F.R.S. 1866. P. 14S. 



