THE TAPEWORM LARVAE 207 



of moisture and favorable temperature, retain their power to infect 

 for several weeks. In dry locations and under the influence of a hot 

 Sim the period of their vitality is reduced, probably to a few days at 

 most. Eggs, through the mediation of food and water, reaching the 

 digestive juices of sheep and cattle have their shells dissolved, setting 

 free the contained embryos which, on reaching the intestine, penetrate 

 its walls by means of their booklets. From here it is probable that they 

 are passively carried to other parts of the body by the blood and lymph 

 currents. With rare exception, only those embryos which reach the 

 brain or spinal cord continue their development. 



The central nervous system is reached by the embryos about the 

 eighth day after the occurrence of infection, upon the arrival at which 

 location they lose their booklets and transform into small cysts. In the 

 course of their burrowings along the surface of the brain they leave 

 small sinuous tracks which may be found three to five weeks after in- 

 fection, often marked by a yellowish purulent material (Fig. 115). At 

 the termination of these furrows the young bladderworms become 

 stationary, and their development proceeds. 



In five to six weeks the cysts are about 1 cm. (3/8 of an inch) in diam- 

 eter and the heads have begun to appear, these attaining their full 

 development in ten to thirteen weeks. The cysts continue to grow 

 until they have reached a diameter of from 3 to 5 cm. (1 3/16 to 2 inches), 

 during which time new heads are in process of formation (Fig. 116). 

 Heads in various stages of development, therefore, may be found in the 

 same vesicle. 



Tabular Review of Life History of Multiceps Mxilticeps 

 Adult Tapeworm in intestine of dog. 



Egg. — Expelled from intestines. 



I 

 Hexacanth. — Freed from egg in digestive tract when 



I ingested by 'sheep. 



Acephalocyst. — In brain or cord of sheep, 



Ccenurus (Polycephalic cyst). — Same. 



Scolex. — -Attached to intestinal wall of dog after in- 



I gestion of cyst. 



Adult Tapeworm. — In intestine of dog. 



Post-mortem Appearance. — In chronic cases there are usually one 

 or more cysts, rarely as many as six, though cases are recorded in which 



