Roijal Microscopical Society. 7 



II. — Further Researches into the Life History of the Monads. 



By W. H. Dallingee, F.E.M.S., and J. Drysdale, M.D. 



{Read before the Royal Microscopical Society, Dec. 3, 1873.) 



Plates XLVI., XLVII., and part of XLVIII. 



No. II. 



In pursuing our researches we have become practically convinced 

 of the importance of what we have theoretically assumed — the abso- 

 lute necessity for prolonged and patient examination of the same 

 forms. Two observers, independently of each other, examining 

 the same monad, if their inquiries were not sufficiently prolonged, 

 might, with the utmost truthfulness of interpretation, assert opposite 

 modes of development. Competent optical means, careful inter j)re- 

 tation, close observation, and time, are alone capable of solving the 

 problem. 



It is no matter of surprise to us that fission has been so gene- 

 rally accepted as the entire method of increase among the extremely 

 minute monads. It is an accurate statement of facts, so far as they 

 go ; but in no case that has been persistently inquired into by us 

 has it proved the essential method of multiplication. Nor has 

 fission itself, in these exquisitely minute forms, been described with 

 sufficient care. It is not a mere division of undifferentiated sarcode 

 into two parts. Before separation takes place there is always a 

 germination of the anatomical elements, which make the new 

 monad complete ; while in many instances the fission is preceded 

 by a suddenly induced amceboid condition. The form we are about 

 to describe will illustrate these points. 



It is a form found in the maceration referred to in our last, when 

 in a more advanced condition of decay. It is extremely various 

 in size ; but averages from the 3000th to the 4000th of an inch in 

 long diameter. Its general aspect is shown in Fig. 1, PI. XLVI., 

 where it will be seen it is a jlong ovate form, pointed at one end, 

 and possessed of two flagella, one (a) permanently hooked, the other 

 (b) gracefully flowing in curves behind. They swim rapidly, but 

 by a series of jerks or springs following each other in constant suc- 

 cession, and coincident with the movements of the hooked flagellum, 



EXPLANATION OF PLATES XLVI., XLVII., and part of XLVIII. 

 Figs. 1 to 4.— Earlier stages of fission in monad. 



„ 5 „ 9. — The process of actual division and formation of reserved fiagella. 



„ 10 ,, 20. — Tlie process of genetic reproduction. 

 Fig. 21. — A monad genetically produced with the hooked flagellum not com- 



plctcly formed. 

 Figs. 22 to 28. — The process of genesis when more than a pair of monads copulate. 



