264 Transactions of the 



being placed anteriorly. The average lengih of the long diameter 

 of the body is the 1100th of an inch. The flagella are about twice 

 the length of the body, very fine, and intensely rapid and graceful 

 in their movements. They are inserted into a couple of pear-shaped 

 bodies, with their thickest ends in contact with the investing mem- 

 brane. They are shown as they generally present themselves in 

 Fig. 1, d, but they also assume the conditions drawn in Fig. 2, 

 being intimately connected with the motion of the flagella ; this 

 may be distinctly seen when the motion of the monad becomes 

 slower, a, h, e, and d show some of the positions assumed, and their 

 relations to the movements of the flagella. 



The motion of this monad when in complete activity is ex- 

 tremely graceful, almost swallow-like ; but there is no question left 

 upon our minds that it is wholly accomplished by means of the 

 flagella. They are usually thrown out in the manner of a swim- 

 mer's arms, and made to meet at the posterior end of the monad ; 

 but they can also be used in all directions, either singly or together, 

 giving either a rolling forward motion, or a gyrating horizontal 

 motion, or even a longitudinal revolution. They can also move 

 backwards, by uniting the flagella and making a sculling motion. 



To attempt to give anatomical explanation of their movements 

 as produced by what appears to be a mere mass of structureless 

 sarcode would be waste of space. But we are constrained to indi- 

 cate what was seen twice by both of us, and three times by one, as 

 indicating something that suggests structure. We were observing 

 once with the Ath, and once with the 2Vth, when we perceived by 

 careful focussing what is drawn in Fig. 3, where the rod a seemed 

 to run longitudinally through the monad as if for support ; the 

 bulbous part h was closely connected with the knobs c, which give 

 actual support to the flagella. 



The posterior part of the sarcode is always filled with granular 

 masses of protoplasm to nearly the extent of half the body, as seen 

 in Fig. 1. These, as we shall subsequently see, play an important 

 part in the life history of the creature. Immediately above this 

 granular mass is situated a nucleus-like body ; it is without struc- 

 ture, and large in proportion to the size of the monad, always 

 occupymg the same position, a, Fig. 1. Beside these peculiar 

 features this creature possessed almost constantly the snapping eye- 

 spots which we have shown to belong to other monads, and have 

 fully described in earlier communications,* but the function of 

 which we have failed to discover. 



We may now consider the phenomena attending the develop- 

 mental history of this form, which is divisible into three chief 

 features. 



(1.) By continuous observation on the normal form, with a 

 * 'M. M. J.; vul. xi, p. 8. 



