366 University of California Publications in Zoology [Vol- 19 



worms and sixty-five partly grown worms of Echinostoma revolution 

 were found in the intestine. Upon careful study the adults from both 

 sources were found to be of the same species. 



The half grown adults 3.80 mm. long were found to have a few 

 eggs in their uteri. 



Perhaps the most significant thing about the adult Echinostoma 

 revolutum as compared with its cercaria, is that the number of collar 

 spines, forty-three, is not carried over in total number to the adult, 

 The adults have only thirty-six or thirty -seven collar spines. In those 

 with thirty-seven collar spines the last one on one of the sides is only 

 about one-third the size of the others. In those with thirty-six spines 

 this small spine is lacking. This reduction in number of spines from 

 the cercaria to the adult, I beileve, can be readily explained by the 

 ease with which any of the spines can be lost unless the worms are 

 handled very carefully, and the fact that there is not enough room 

 on the collar for more spines. The spines in the adult are arranged 

 in alternate rows as in the cercaria and also have the same clumping 

 arrangement on the ventral side, but the number in each clump in the 

 adult is reduced about three on a side. The size of the innermost 

 spine, the very small one above mentioned excluded, is usually about 

 two-thirds the length of the larger ones, which are 0.099 mm. in length. 

 Since the largest spines on the collar of the cercaria are only 0.018 mm. 

 long this means that the majority of the collar spines have grown 

 about five and a half times. This explains the fact above stated that 

 there is not enough room for the total number of spines on the adult 

 collar when compared with the increase in size of the collar of the 

 adult over the cercaria. The collar of the cercaria measures about 

 0.125 mm. in diameter while the collar of the adult only measures 

 0.495 mm. 



The body spines of the adult are much like those of the cercaria 

 (fig. 45) but have increased about four times in size, those on the side 

 between the oral and ventral suckers measuring 0.025 mm. in length. 

 The arrangement of the body spines is also the same. Ventrally, 

 between the oral and ventral slickers, the spines almost completely 

 cover the body. On the sides of the ventral sucker, blunt irregularly 

 arranged spines were also found. 



The great increase in the size of the ventral sucker is an outstand- 

 ing fact. In the cercaria it is 0.094 mm. in diameter, whereas in the 

 adults 8 to 10 mm. long it averages about 1.075 mm. in diameter. The 

 size of the oral sucker, however, has increased only from 0.072 to 



