134 DISEASES OF DOGS. 



forms varying with their age. Thus those nearest the head are the 

 youngest, and those at the other extremity the oldest. It is these 

 last which one sees from time to time pass with the fsecal discharges. 

 They are, in fact, the ripe segments, or proglottids (Eig. 23), which 

 detach themselves from the hind portion, and each portion thus freed 

 is endowed with reproductive organs. In time these detached por- 

 tions die away, hut the eggs contained in them have heen im- 

 pregnated by spermatozoa, and simply await another host to begin 

 anew the cycle of existence. The eggs thus scattered broadcast are 

 not influenced by extremes of heat or cold, dryness or moisture, nor 

 does Time seem to desti-oy their germinating power. From this it 

 will readily be seen how important it is to bum all excreta from 

 dogs infested with tapeworms. 



In course of time the eggs are swallowed by a suitable host — 

 sheep, rabbit, pig, or ox — each of which has its particular form of 

 tapeworm. The gastric juices of this intermediary soon dissolve the 

 outer covering of the egg, and an embryo, oval in form, and pro- 



FiG. 23. Proglottid, or Eipe Segment op Tapeworm, showing the 

 Sexual Organs. 



vided with six bristle-like organs, or stylets, results. By means of 

 these the embryo is able to penetrate the tissues of its host, and to 

 take up its position in whatever part of the animal's body Nature 

 has ordained that it shall flourishT-it may be in the brain of the 

 sheep, where it assumes the form of a bladder — becomes encysted 

 (Fig. 24). Gradually the stylets, which afforded it the means of 

 access, decay, and a circle of hooks is developed, by which the future 

 Tapeworm will be enabled to anchor when in its new host. 



Soon a many-headed animal (Fig. 25) develops. A fresh host is 

 now necessary to carry on the cycle. In the case of the gid tape- 

 worm the sheep dies or is killed, and in due time the cysts are 

 swallowed by the dog. Once in the dog the bladder is absorbed, 

 and the tapeworm matures. The heads are set free, and the 

 creatures having made their way into the intestines, attach them- 

 selves thereto, and each one is capable of founding a colony, as it 

 were. The head has no mouth, but is provided with sucker-Eke 

 processes (Fig. 26), through which the animal derives sustenance. 



