298 



STATE BOARD OF AGKICULTURE. 



Fig. 1. 



from which we procured, through the courtesy of the author, the cuts iUus- 

 trating this article. 



I have ah'eady stated that it was impossible to define the class worms, as some 

 of the species so mimic, even in structure as well as form, some of the species 

 even of the other hranclies, such as vertebrates, mollusks, and radiates, that 

 some authors in their classifications have put them in such conipany, while 

 many that are generally regarded as belonging to other branches are now classed 

 among worms, and that too by some of our first naturalists. In fact it is well 

 nigh impossible to give a positive definition to any group of animals, which of 

 course is easily understood if all animals have a common parentage. 



To give the orders of worms that contain all the parasitic species is likewise 

 difficult, as there are as many plans as there are authors. The following is 

 simple, and perhaps as satisfactory to our purpose as any : 



1. Cestodes. This order includes the tape worms and their immature forms, 

 measles and bladder worms, and are found quite generally in vertebrates, insects, 

 and mollusks. 



These animals, though destitute of a mouth and digestive apparatus, pos- 

 sesses a true head, with hooks by which they maintain their hold. The remain- 

 der of the body is, when mature, comp)osed of a series of joints, Avliich finally 

 separate, when each exists for a season. Each of these joints possesses sex 

 organs, both male and female, and in them the young develop. These are 



sometimes many feet in length. The Toe- 

 nia solium (Fig. 1) has been taken from 

 the human intestine, to which it is confined, 

 and found to measure fifteen feet in length. 

 Head and a portion of the body of Solium, and to be Composed of 800 joints. Hcuce we 

 understand their almost unparalleled fecundity. The broad tape worm of man ex- 

 ceeds 30 feet in length, possesses 10,000 joints, and may produce 10,000,000 young. 

 As examples of tape worms we have those of the hog and of cattle, which 

 when young are the measles of human flesh, and pork, and cattle respectively, 

 and when old are found in the human intestines ; several tajie worms of the 

 dog, known as the bladder worm of sheep and cattle ; the water brain of sheep, 

 and the hydatid tumors of man, of sheep, and cattle, respectively, when in the 

 young state. All of these in the young state are fatal when abundant, and 

 doubtless the cause of more deaths among men and our domestic animals than 

 we have even dreamed of. Many of the very worst of these are spread and 

 developed through the agency of dogs. Prof. Yerrill well says : " It is perfectly 

 safe to say that at least twenty-five sheep are killed by parasites derived from 

 dogs for every one killed by the teeth of dogs ! It is also safe to say that more 

 than fifty persons die from the same parasites for every one that dies of hydro- 

 phobia ! And yet this work of destruction goes on silently and almost unob- 

 served, except by professional men, week after week and year after year. The 

 loss of human life every year more than counterbalances all the good that all 

 the dogs in the civilized world can possibly do." 



The second order is Trematodes (Flukes). The flukes are flat worms 



(Fig. 3) without distinct joints, and are often 

 found in both vertebrate and invertebrate ani- 

 mals. They have a complete alimentary canal, 

 except that it is closed opposite the mouth. One 

 or tw^o large vessels empty near the posterior of 

 the body, which arise from the union of smaller 

 vessels, and these from still smaller, till at last 



Fig. 2. 

 Fasciola ftepaa'ca.— Sheep Fluke. 



