GENUS POLYTOMA. 303 



ascertained. A third or true genetic form of reproduction dependent on the intimate 

 fusion or coalescence of two individuals followed by encystment and the breaking up 

 of the amalgamated zooids into countless almost invisible spores (see PI. XV. 

 Figs. 77 and 78), as already described of Monas Dallingert, Cercomonas typicus, and 

 Heteromita rostrata, completes the life-cycle of this remarkable species as observed 

 by these indefatigable investigators. 



A few structural peculiarities of this type referred to by Messrs. Dallinger and 

 Drysdale, demand brief notice. The so-called "snapping eye-spots" situated in the 

 anterior region of this form, and reported to be present in many other monads 

 examined by them, though they failed to determine their precise import and function, 

 represent undoubtedly the characteristic contractile vesicles already recognized by 

 Schneider and other earlier writers. Under certain conditions the two anterior 

 flagella were further pronounced by these investigators to be replaced or supple- 

 mented by two knob-like structures, mounted on slender pedicles, and to which 

 phase of the monad they therefore applied the title of the " clubbed condition." 

 It was at first supposed that this condition was intimately connected with some 

 special reproductive process, the question ultimately, however, being left undecided. 

 Schneider, nevertheless, had previously maintained that the knob-like processes 

 represented the flagella as withdrawn or shortened previous to encystment. Even 

 under normal conditions the existence of fusiform or pear-shaped inflations of the 

 bases of the flagella is recorded, these inflations being further interpreted as playing 

 an important part in the function of natation, and as possessing apparently a 

 muscular property. The swimming motions of Polytoma are described by Messrs. 

 Dallinger and Drysdale as very graceful and swallow-like ; the flagella being thrown 

 out in the manner of a swimmer's arms and made to meet at the posterior end of the 

 monad ; these appendages can likewise, they report, be used in various other ways, 

 producing a rolling-forward motion, a gyrating horizontal one, or even a longitudinal 

 revolution. 



Quite recently, January 1880, the author had the opportunity of examining 

 living samples of Polytoma uvella as developed abundantly in animal macerations 

 at the Biological Laboratory, South Kensington. The data thus independently 

 derived have thrown an entirely unexpected light on the phenomena previously 

 recorded, concerning the so-called knob-like or pyriform inflations at the base of the 

 flagella, as observed by Schneider and Messrs. Dallinger and Drysdale. It has been 

 definitely ascertained by both the examination of living monads and of examples 

 killed with iodine and osmic acid, that what these authorities took for independent 

 knob-like or fusiform developments are actually minute loop-like flexures of the 

 basal region of the flagella, as shown in Figs. 67-69 of Plate XV. The substance 

 of the flagella throughout this region is softer and more adhesive than in the 

 remainder of their length, and it is by this loop-like flexure that the animalcules 

 attach themselves to the glass or other neighbouring objects as first observed by 

 Schneider, and may thus ride securely anchored, during the passage around them of 

 even a considerably forcible current. It is certainly a very remarkable circumstance 

 that this capacity of attaching themselves, so abundantly displayed in the specimens 

 recently examined, should have entirely escaped the many hours' observation of Messrs. 

 Dallinger and Drysdale, who have described them only as motile or free-swimming 

 animalcules. In both the examples examined by the author on the occasion quoted, 

 and still more recently, it was observed, indeed, that the attached condition is the 

 more normal one, but few, unless purposely disturbed, exhibiting their natatory 

 properties two minutes after their transfer to the field of the microscope. The 

 existence of the loop-like flexures at the bases of the flagella, discovered by the 

 author, explains readily the several apparently anomalous features concerning the 

 type, noticed in the accounts given by previous investigators ; thus the so-called 

 " clubbed " condition of the animalcule, as reported by them, was repeatedly recog- 

 nized, but was demonstrated to be the optical image, produced under high magnifica- 

 tion, of the basal portion of the flagellum with its loop-like flexure only being in focus. 

 Under slightly modified conditions, again, the loop-like flexures and the remaining 

 length of the flagella being clearly visible, the divarication of this latter portion may 



