166 NATURAL HISTORY 



their not being shortened in the contractions of the 

 animal, but assuming a serpentine form, being appa- 

 rently passive. That they are not vessels is also evident, 

 because no pulsation or circulating fluid has ever been 

 perceived in them ; hence, by fair reasoning, we may 

 safely conclude they form a nervous system ; and it is well 

 remarked by Mr. Johnston*, that according to all our 

 ideas of known physiological laws, the existence of active 

 voluntary motion presupposes the necessity of an ani- 

 mating nervous system. Hitherto, however, no attempt 

 has been made to prove its existence ; but as these ani- 

 malcules are excluded, by the delicacy and minuteness of 

 their forms, from the ordinary means of investigation, 

 still the transparency of their tissues has enabled us to 

 discover a muscular system in them, and has led to the 

 more than probable notion that there exists also its neces- 

 sary appendage, a nervous one. 



Having in the descriptions of the preceding genera 

 and species shewn the singular and varied methods by 

 which their production is maintained, — such as their pro- 

 pagating by a division of the animalcule, when arrived at 

 maturity ; by buds from the parent, like plants, as in the 

 Vorticella convallaria, in some states of its existence ; and 

 by spawn, as in the Kolpoda cucullus, — we now arrive at 

 a being which may be said more closely to resemble the 

 higher orders in the animal kingdom. This animalcule 

 is an hermaphrodite (//), the ovarium being united 



* Edinburgh Philosophical Journal. 



