234 ORDER FLAGELLATA-PANTOSTOMATA. 



the phenomena elicited, and represents, indeed, the only member of the genus Monas 

 par excellence, as here recognized, with whose entire developmental manifestations 

 we are at present conversant. 



The reproductive phenomena of this particular species, as reported by Messrs. 

 Dallinger and Drysdale, may be briefly epitomized as follows. The extraordinarily 

 rapid multiplication of this type being unaccounted for by the ordinary process 

 of transverse fission, or by the production of minute spores requiring time to 

 develop to maturity, a further investigation elicited that under certain conditions 

 there intervened a supplementary process of fission, by which as many as from 

 thirty to sixty individuals of appreciable size were produced from a previously 

 single zooid. The indications given by an individual about to increase by this 

 multiple mode of fission were its adoption, first, of a somewhat rounded outline, 

 then of a more irregular and slightly amoeboid form, and finally of a simple 

 spheroidal contour. In this last condition only, the flagellum disappeared, and the 

 animalcule entered upon a perfectly quiescent or encysted state. Patiently watched 

 with an amplification of about 3000 diameters, a cruciform mark or constriction 

 was observed to appear suddenly, dividing the sphere into four equal portions 

 (PL XIII. Fig. 3), other divisional lines quickly following, until the entire body was 

 partitioned by deep curved indentures with innumerable segments. An active 

 whirling motion of the sarcode then ensued, lasting from ten to as many as seventy 

 minutes, and at the end of this period it broke up into numerous sausage-shaped 

 bodies as shown at Fig. 5. These now exhibited a quick writhing motion upon each 

 other, which lasted for a space of seven to thirty minutes, the whole mass finally fall- 

 ing to pieces or detaching itself separately as uniflagellate monads, identical in shape, 

 though of smaller size, with the original or parent animalcules. No separate investing 

 membrane or indurated cyst was at any time associated with this process of multipli- 

 cation, the separate segments being held together until the time of their final libera- 

 tion by mere cohesion of their constituent sarcode. Reproduction by spores, pro- 

 duced by the genetic union or coalescence and encystment of two individuals, was 

 likewise ascertained by Messrs. Dallinger and Drysdale to play an important part in 

 the developmental life-cycle of this form. The zooids upon whom this special and 

 more important mode of propagation devolves are of slightly larger size and more 

 rounded outline than the ordinary forms ; the anterior extremity, or that nearest to 

 the flagellum, is also conspicuously and coarsely granulate.* Moving among the 

 smaller animalcules, they fix themselves to one of these as shown at Fig. 7, and the 

 two swim about joined to one another for a considerable interval. The smaller 

 monad is at length completely absorbed into the substance of the larger one, whose 

 movements now become sluggish, and terminate in its assumption of a slightly 

 flattened subspherical and encysted state (Fig. 8). The encystments, after remaining 

 quiescent for about thirty-six hours, open slowly, liberating, as shown at Fig. 9, what 

 appears to be merely a glairy fluid, differing slightly in density only from the surround- 

 ing water. Examined with the highest available amplifying glasses that is, a -^-inch 

 objective, with a magnifying power of from 2500 to 15,000 diameters, no granular 

 composition indicating the presence of spores could be detected in the discharged 

 fluid, but in about seven hours after its emission minute points, hitherto too small for 

 detection, made their appearance, and rapidly increased in size. Movements in 

 these granular points were detected in the course of the next five hours, and soon 

 after this they swam off, corresponding in all respects, except for their slightly smaller 

 size, with the typical monads from whence they originally sprang. 



Monas fluida, Duj. PL. XIII. FIGS. 10-18. 



Body soft and semifluid, exceedingly variable in shape ; its most 

 regular contour elongate-ovate or subcylindrical, with the length equal to 

 about three times the diameter, but more frequently widest anteriorly, 



* By accident the artist has omitted to reproduce the more coarsely granular aspect of the 

 anterior region. 



