I02 UNDKRHII.L : 



this development the cyst pushes tlie tissues aside to make 

 room for itself, and, throujjh the irritation produced, an outer 

 cyst wall is formed, made up of the connective tissue of the 

 host, the complete orj>anism or bladder worm {Cysticercus 

 bovis) thus formed having consumed a period of time from 

 the release of the embryo variously estimated at from seven 

 to eighteen weeks. If the host animal is slaughtered before 

 the Cysticercus becomes calcified, which stage of degeneration 

 will be reached in about six to eight months from the inva- 

 sion, and the incompletely cooked meat be used by man for 

 food, the cyst, upon arriving in the stomach, is digested 

 away, the head and neck (scolex) alone remaining uninjured. 

 The scolex then passing into the small intestine, fastens to 

 the wall by means of the suckers with which its head is pro- 

 vided, obtains nourishment by absorbtion of nutrient intes- 

 tinal fluids of its host through the general surface of its body, 

 and proceeds to give rise to segments by transverse division 

 tlirectly back of the head and neck ; thus developing the stro- 

 bila, or colony of sexually mature proglottids, similar to that 

 of the ancestor from which the cycle started in the intestines 

 of a previous human host. Here then is ati animal well 

 showing the degree of degeneration which may be reached 

 in extreme parasitism ; there are no organs of locomotion, no 

 organs of special sense, no organs of digestion, no organs of 

 respiration, and none of circulation. The body consists of a 

 long band of connected segments, each bisexually complete, 

 and in itself a sort of independent reproductive animal, the 

 entire energy of the organism concentrated upon the function 

 of reproduction, that the perpetuation of the species may be 

 insured amid the perils with which this process is beset. 



In many forms permanently parasitic there is an early 

 period of development in which organs of locomotion are 

 distinctly present, but, as the animal matures, these fail to 

 develop or become lost. If we assume that this gradual loss 

 of organs, change of structure, and protective transmission 

 of the embryo to an intermediate host is due to the parasitic 



