238 SOME MINUTE ANIMAL PARASITES 



the other hand, it must be remembered that any 

 parasite of an animal that utilizes even the smallest 

 portion of food destined for the nourishment of that 

 host is depriving the latter of its nutriment to the 

 extent of the food absorbed. Hence it is really 

 incorrect to speak of any parasite as harmless or 

 blameless. 



The majority of the Myxosporidia possess a some- 

 what massive protoplasmic body when full grown, 

 and within the body at any stage of its life either 

 two large spores or many small spores are produced. 

 The number of spores formed has been used as a 

 basis of classification, and the groups Disporea and 

 Polysporea result. The spores are the means of 

 continuing the life of the organism. They possess 

 a complicated structure which will be detailed later, 

 but from each one a small amcebula issues when the 

 spore is favourably situated. This occurs in the 

 case of fish parasites, when the spores swallowed 

 with food or water enter a new host, and the diges- 

 tive juices found in the intestine act upon the spore 

 coat, or sporocyst. The amoebula may enter a cell 

 of the host's food-canal, or may pass into the diver- 

 ticula of the food-canal, sometimes reaching the gall- 

 bladder. Perhaps by way of the blood-stream it 

 may reach the urinary bladder of the host, or, as in 

 other cases, it can attack the musculature and even 

 the nervous system. Wherever it penetrates, the 

 course of development is much the same. The para- 

 site increases greatly in size, and during its trophic 

 existence feeds passively to a large extent on the 

 semi-fluid media by which it is surrounded. While 



