GENUS PHYLLOMITUS. 299 



show no trace of the spiral convolutions which distinguish the adults, but are 

 simply elongate and compressed ; later on a single spiral flexure is developed, and 

 it is not until the most mature and active natatory condition is arrived at that its 

 characteristic highly convoluted contour is attained. In that intermediate phase 

 in which the animalcules exhibit but one spiral twist, the body is comparatively 

 short, about three times as long as broad, with rounded extremities, and presents 

 a considerable resemblance to Pertys Spiromonas volubilis, last described. A pro- 

 longed investigation of this species elicited that it possesses a temporarily fixed as 

 well as an active swimming stage, the animalcules at such time attaching themselves 

 by the extremity of the posterior of the two flagella, and fishing in the surrounding 

 water with the anterior one, after the manner of an ordinary Heteromita or Aniso- 

 nema. It was further observed that under these conditions the spiral convolutions 

 were relaxed, sometimes one only being represented, and in others disappearing 

 altogether. On becoming detached and resuming the free-swimming state the 

 spirally convolute contour is again adopted. At the end of a few hours almost the 

 whole adult individuals of the colony under examination were seen to assume an 

 amoeboid phase, and to crawl actively over the surface of the glass by the aid of their 

 pseudopodia. Some of these coming in contact with their fellows immediately fused 

 or coalesced, forming subsequently spherical encystments which later on broke up 

 into minute spore-like bodies. The single zooids likewise formed similar but smaller 

 encystments, and dividing by multiple fission into two or four segments only, were 

 subsequently liberated as units resembling the unconvolute earlier stages of the 

 parent monads. The motion through the water of the adult animalcules is regular 

 and even, consisting of progress in a straight line, the body turning on its long axis 

 in a screw-like manner, both flagella actively vibrating in advance. In the younger 

 examples the movements are eccentric and vacillating, the animalcules first advanc- 

 ing straight forward for a short distance, and then turning round and returning to 

 the point from whence they started. Their motion in this respect somewhat resembles 

 that of various species of Vibrio or Spirillum, The so-called Bodo grarilis, merely 

 figured by Stein in his recently published volume, without a word of explanatory text, 

 must undoubtedly be regarded as a synonym of this species. 



GENUS IV. PHYLLOMITUS, Stein. 



Animalcules free-swimming, variable in form, more or less ovate ; 

 flagella two in number, produced from the anterior extremity, unequal in 

 length and united to one another throughout their basal portion ; no 

 distinct oral aperture. 



The single species referred to this genus is figured without an accompanying 

 description in Stein's recently issued volume, the present diagnosis of both that 

 species and the present newly instituted generic group having to be framed from 

 his delineations. 



Phyllomitus undulans, Stein. PL. XV. FIGS. 47 AND 48. 

 Body elongate-ovate, variable in form, three or four times as long as 

 broad ; sometimes straight and rounded, and sometimes sharply pointed and 

 recurved posteriorly ; flagella united basally for a distance exceeding one- 

 half of the length of the body, forming in this region a ligulate or strap-like 

 prolongation, the shorter flagellum produced separately but a little distance 

 beyond the distal termination of this ligulate prolongation, the longer one 

 fine and undulating continued for a length exceeding that of the entire 

 body ; the anterior extremity of the ventral region immediately beneath the 

 insertion of the flagella exhibiting an oval excavation ; endoplast anteriorly 



