RESEARCHES IN HELMINTHOLOGY AND PARASITOLOGY. 23 



the superior cell, which is entirely passive. The superior cell is also 

 frequently drawn or contracted within the inferior, and again pro- 

 truded by the contraction of the latter, and the propulsion of the 

 granular contents against it. The inferior cell is also frequently, 

 more especially in younger individuals, intussuscepted within itself 

 through a partial contraction ; and again relieved by a general con- 

 traction of the cell-wall. 



In the state in which Grcgari7ia is found, it would probabl}' hold 

 a rank between the Trematoda and Trichina, the lowest of the Nema- 

 toidea. 



Nydothems,'^'- a new genus of Polygastrica, allied to Plescoiiia. — 

 Body ovate, dilated posteriorly, compressed anteriorly, granulated, 

 longitudinally lined, with an apparent operculum covering its an- 

 terior half, and having a semicircle of cilia just within its margin 

 inferiorly and posteriorly. Center of the operculated portion fur- 

 nished with a large trapezoidal finely granular areola. Posterior part 

 of the body with a short fissure passing inwards and downwards. 



Nydothcrus vclox. — Body white, ovate, conoidal, anterior margin 

 rounded, obtuse ; posteriorly acute. Posterior margin of the ap- 

 parent operculum passing in a curved line upwards upon the middle 

 of the body to within a short distance of the back, and furnished in- 

 feriorly with a point projecting backwards, with a line passing 

 down from the back about the middle of the operculum to the trape- 

 zoidal areola, giving the part of the body anterior to this the appear- 

 ance of a head. Trapezoidal areola, with curved sides, finely 

 granular. Posterior fissure communicating with the exterior, just 

 above the acute termination of the body, and passing inwards and 

 downwards, resembling an anal aperture. Areolae of the interior 

 sarcous mass generally minute, one large and round pretty con- 

 stantly to be observed at the inner termination of the posterior 

 fissure. 



Length from i -254th to i-i8oth inch; breadth from i -320th to 

 I -25 4th inch. 



Habitat. — Commencement of the large intestine of Juliis margi- 

 natus, often found in considerable numbers. 



Remarks. — This genus is closely allied to Plesconia, but possesses 

 no appendages excepting the semicircle of cilia, just within the edge 

 of the apparent operculum. 



The animal swims in water with great ease and grace. After 

 being in this fluid some time, the external investment bursts, and 



Nyctotherus : — No-/To6y]pa<i. 



