368 University of California Publications in Zoology [Vol. 19 



Looss (1899, p. 684) sums up the discussion concerning the knowl- 

 edge of this species and, in my opinion, places at least two different 

 species together. In the first place the hosts in which he finds the two 

 types are quite different. One type he finds in a shore bird of the 

 Limicolidae, Machetes pugnax; the other he finds in the domestic 

 goose. If this were the only difference it would hardly be enough to 

 make two distinct species, since specificity of hosts is probably not as 

 great as is usually believed. But the number of collar spines is found 

 to be entirely different also. The echinostome found in the goose has 

 thirty-seven spines, while the one from the shore bird has but thirty- 

 four spines. Furthermore, the length, the shape, and the arrangement 

 of the spines are entirely different. In one the smaller inner ventral 

 spines are not present. The clumping or crowding of the ventral 

 spines on each side is to be found in one and not the other. The range 

 of variation in egg size is also different. One range of variation is 

 from 0.092 to 0.134 mm., the other from 0.101 to 0.111 mm. 



Since Echinostoma revolutum was first found by Froelich in the 

 goose, and later by Zeder, Looss and others, including myself, in the 

 goose and duck, the type with the thirty-seven spines, I think, should 

 be called by the above name and a new name chosen for the one with 

 the thirty-four spines found in the shore bird, Machetes pugnax. I 

 suggest the name Echinostoma limicoli. The large number of primary 

 hosts assigned to this species by different workers I feel quite sure is 

 due to placing two or more species under the one name. 



THEORETICAL DISCUSSION OF THE LIFE CYCLE 



Briefly stated the stages of the life cycle of Echinostoma revolutum 

 are these : egg. miracidium, mother-redia, daughter-redia, cerearia, 

 encysted agamodistome (cyst) and adult. To accomplish this life cycle 

 only two hosts are necessary, the snail Physa occidentalis and a duck 

 or goose. Apparently any duck and perhaps any goose forms a suitable 

 host, since the adult echinostomes were raised experimentally in 

 mongrel ducklings, were found in the American scaup duck, Marila 

 marila, on Stow Lake, and have been reported from many other ducks 

 and geese in many places in the northern hemisphere. As stated, 

 Physa occidentalis usually serves as both the intermediate and second- 

 ary intermediate host. This stage, however, is not specific, since the 

 encysted agamodistome stage has also been found in anothe.r species 

 of snail and in Planaria. 



