158 Miscellan eous . 



liker to submit the Gregorince to fresh observation. The following- 

 are the conclusions at which he arrives in his last memoir : — 



1. The Gregorince are animals. 



2. The simple Gregorince are decidedly composed of a single cell. 

 Their membrane corresponds to the cellular membrane ; their con- 

 tents are those of a cell ; the vesicle which it contains represents the 

 nucleus ; the granulations (sometimes there is only one) of the latter 

 are simple or disaggregated nucleoli. These simple Gregorince are 

 only met with in Annelides. ', 



3. The Gregorince with constricted body most probably correspond 

 also to a simple cell of a peculiar form. They are met with in in- 

 sects and Crustacea. 



4. There is no reason for not considering the Gregorince as animals 

 which have attained their most perfect state. 



5. The cases of pseudo-navicellae with granular contents and with 

 vesicles probably proceed from a transformation of the Gregorince. 



6. The presence of two nuclei or of two cells in the interior of 

 certain Gregorince indicates either the commencement of their repro- 

 duction or their transformation into pseudo-navicellae. — Zeitschrift 



fur Wissenschaftliche Zoologie, i. p. 1 . 



Nyctotherus, a new genus of Polygastrica allied to Plesconia. 

 By Dr. Leidy. 



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 in- 

 feriorly and posteriorly. Centre of the operculated portion furnished 

 with a large trapezoidal finely granular areola. Posterior part of the 

 body with a short fissure passing inwards and downwards. 



Nyctotherus velooo. Body white, ovate, conoidal, anterior margin 

 rounded, obtuse ; posteriorly acute. Posterior margin of the apparent 

 operculum passing in a curved line upwards upon the middle of the 

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

 with a point projecting backwards ; with a line passing down from 

 the back about the middle of the operculum to the trapezoidal areola, 

 giving the part of the body anterior to this the appearance of a head. 

 Trapezoidal areola with curved sides, finely granular. Posterior 

 fissure communicating with the exterior, just above the acute termi- 

 nation of the body, and passing inwards and downwards, resembles 

 an anal aperture. Areolae of the interior sarcous mass generally 

 minute, one large and round pretty constantly to be observed at the 

 inner termination of the posterior fissure. 



Length from l-254th to l-180thin. ; breadth from l-320th to 

 l-254th in. 



Hab. Commencement of the large intestine of Julus marginatus, 

 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 



