623 



Plana, and Krabbe) are very slight and can for the most part 

 be explained by contraction, insufficiency of material, and lack 

 of details. The description of the hooks of the suckers of T. 

 echinobothrida (as being so simple) should, I believe, be taken 

 with reserve. The hooks are very small and are not easily 

 studied. The fact that the genital pores are described as ir- 

 regularly alternate by Megnin and unilateral by Plana and 

 Krabbe is not, in my opinion, a serious difference in this genus. 

 This opinion, radical as it may appear, is based upon the fol- 

 lowing observations: 



The worms which Dr. Moore found producing a nodular dis- 

 ease in chickens give rise to the same pathological conditions 

 as the form described by Plana, and agree with Piana's species 

 in regard to the armed rostellum, the form and size of the 

 hooks, both on the rostellum and suckers, and in almost every 

 other character mentioned by Plana. The genital pores vary 

 in different specimens. In some specimens they are entirely 

 unilateral; in other specimens all but one or two may be on 

 the same side of the worm; in fact it is often necessary to 

 mount the entire strobila before it is possible to find an al- 

 ternating pore; in still other sipecimens the pores are extremely 

 irregular. The specimens with irregularly alternate genital 

 pores agree in all other respects, so' far as I can see, with 

 Piana's form. The only difference between these specimens 

 and Megnin's description appears to be (1) the num.ber of 

 hooks upon the rostellum (Megnin estimates them at about 

 100, the American forms possess ca. 200-20S); (2) the form of the 

 hooks on the suckers (possibly due to misinteipretation as the 

 form of hooks Megnin describes is otherwise unknown in this 

 group); and (3) the arrangement of the hooks on the suckers 

 (in Megnin's form the largest hooks are in the center row, in 

 the American form the largest hooks are those of the external 

 row). This latter point of difference should not be given too 

 much weight, as Megnin evidently made no microtome sections, 

 and this point could hardly be established definitely otherwise. 



In short, I incline to the belief that tetragona, echinobothrida, 

 and bothrioplitis all represent one and the same species. 



