116 



The next stage of the einbryonie twnia found was taken from a lamb. 

 In this stage the young worm (about 2""" long) is well outlined. It had 

 a head with four suckers and a short unsegmented body. The next step 

 in the development showed the body segmented. In one or two speci- 

 mens I have seen a little loop with its convex end projecting towards 

 the outside, but have not yet been able to determine its significance. 

 Between these stages and the adult the different steps of development 

 are easily filled in by a study of a single worm. 



Occurrence and distribution. — Although there is a periodicity in the 

 appearance of the broad tape- worms among lambs, causing at times epi- 

 zootic outbreaks, the worm may be found throughout all months of the 

 year in localities where it occurs. No section of the United States 

 seems to be entirely free from it. They have been found in winter, in 

 spring, in summer, and in the fall, in the intestines of iambs examined 

 at the abattoir. They are not so frequent in winter and early spring as 

 at other times, but seem to be more abundant in some localities than in 

 others, though this may be due to unequal opportunities of observation 

 in all places. A less number was found in the West than occur in the 

 East. Conditions of climate and soil also seem to have some influence 

 on the appearance of the tape-worms. Damp, warm climates and 

 heavy, moist soils appear to be more favorable to their preservation 

 while on the ground. But none of these factors would seem so favora- 

 ble to the growth and life of the tcenia as holding the sheep on over-fed 

 pastures, as demonstrated by experiments elsewhere related. 



Differential description^. — Tcenia expansa differs from T. Jimbriata in 

 the method of shedding its segments. Instead of maturing a few of 

 the segments at a time and shedding them, as the latter do, whole sec- 

 tions ripen and pass away, so that an examination of a sheep which 

 has been observed to pass proglottides during a past week will reveal 

 but little more than the head of a worm. The exact length of time that 

 is consumed by the worm in maturing, so that it all passes away, is 

 nndetermitied, but it is nevertheless an important factor in the disease, 

 for after the worm is passed the lambs begin to recover. From what 

 was learned and seen of the disease the opinion was formed that the 

 worms do not retain their adult size more than a month. The heads, 

 which are left, develop slowly and form new adults. They may not 

 cause so much disturbance at this time, however, for the lamb becomes 

 older and better able to withstand them. 



The rate of growth of the broad tape- worm is very rapid as compared 

 with that of Tcenia Jimbriata. This is easily demonstrated by the fact that 

 T. expansa are found 2 to 5 yards long in lambs from two to four months 

 old, while T. Jimbriata are scarcely as many inches long in lambs of the 

 same age. If we suppose the Iamb to become infected during the first 

 month, of its life, the age of the tcenia in the above lambs would not be 

 over three mouths, which would give an average growth of nearly a 

 yai'd per mouth. This enormous increase in size is an important factor 



