578 DESCKIPTION OF IPolt/i^ustrica. 



Genus Nasstjla.. — Body covered with cilia, ovoid or oblong, turgid 

 and prominent in front, but without the expansion or beak on one 

 side ; mouth lateral provided with a circlet of teeth, in the form of 

 a wheel (Nassa). I^umerous polygastric cells are seen, and in two 

 species the discharging orifice. Ehrenberg states that the existence 

 of a new system of organs subservient to digestion becomes evident 

 in this genus : these are of a violet colour, and probably biliary 

 glands ; one is present in Chilodon ornatus, Burmria vernalis, Tra- 

 clielius meleagris, Amphileptus margaritifer, meleagris, and longicollis ; 

 they resemble the vesicular glands around the stomachs of the 

 Rotatoria. The propagative system is double ; two species have the 

 ova gTanules, and all possess a large oval or spherical gland, and 

 one or more contractile vesicles. Only transverse self-division has 

 been observed. They are found in stagnant water, especially where 

 Conferva and Oscillatoria are present. 



N. elegans. — Body cylindrical or oval, slightly attenuated in front, 

 extremities very obtuse. It is white or greenish, spotted with 

 violet vesicles. Digestive cells, containing Chlamidomonas, or other 

 food, may often be observed ; and from fifteen to twenty rows of 

 cilia may be seen at one view. The animalcule swims backward 

 and forward, turning upon its longitudinal axis. The mouth is 

 easily perceived by the currents, when indigo is mixed with the 

 water : it has a circlet containing twenty-six little wands or teij^h, 

 which can voluntarily diverge or converge anteriorly. When self- 

 division ensues the large central gland divides. Figs. 310 and 311 

 represent this creature; the latter is a young one. Found with 

 Lemna and Conferva. Length 1-1 40th to 1 -120th. 



N. ornata (IST. viridis ? D.) — Body ovate or globular, depressed, of a 

 broA^Tiish-green colour, variegated with numerous violet vesicles. 

 The posterior part of the body has a small excavation. Ehrenberg 

 says there are from six to eight groups of vesicles, forming a wide 

 circle round the mouth ; these are filled with a violet- coloured juice, 

 which is discharged with the excrement, and appears like drops of 

 oil, but soon mixes with and colours the water. Found amongst 

 swimming clusters of Oscillatoria by Ehrenberg. Size to l-96th; 

 ova l-4800th. 



N. aurea. — Body ovato-oblong, neaiiy cylindrical, very obtuse at 



