and their Affinity with the Infusoria flagellata. 17 



cated state during a whole lifetime, I am furthermore sustained 

 in believing by the discovery of some new generic forms, which, 

 although scarcely, if at all, more highly organized than Monas, 

 have in addition such characters as would seem to stand in the 

 way of a transition to a more elevated grade of existence. For 

 instance, the presence of a calyx about the body of an infusorian, 

 into which it can retreat, is an indication of a fixity of condition 

 which corresponds to the ad\ilt state. Thus I found one of the 

 new genera which I have just alluded to. 



Bicosoeca, as it is called, may be described in general terms as 

 a stemless Monas which is attached to the bottom of a calyx by 

 a highly muscular retractile cord. All the organs have the same 

 remarkable definiteness of relationship and peculiarity of form 

 that Monas possesses ; and in addition there is the muscular cord 

 which with oft-repeated jerks retracts the body to the very bot- 

 tom of the calycine envelope. There are two singularly diverse 

 species of this genus — one marine, and the other lacustrine. 



The most interesting infusorian of this group of new forms is 

 the one which I have called Codosiga. This links the Sponges to 

 the flagellate Infusoria. Its greatest peculiarity consists in the 

 possession of a highly flexible, extensible and retractile, mem- 

 branous collar or hollow cylinder, which projects from the ante- 

 rior end of the body. The cylinder is slightly flaring; and if 

 we include the asymmetrical body, the whole might be compared 

 to a very deep one-sided bell, with its narrower end half filled 

 up. The single, sigmoid-arcuate, rigid flagellum arises from the 

 depths of the bell, exactly at the middle of the truncate front, 

 as it were forming a prolongation of the longitudinal axis of the 

 body. There is no lip ; and the flagellum, which rises close to 

 the mouth, has a strong resemblance to that of Monas, both in 

 proportion, form, and habits, and performs the office of a pre- 

 hensile organ when the body is fixed, or acts as a propeller dur- 

 ing natation. The contractile vesicles are two, or even three, in 

 number, and lie in the posterior third of the body. The only 

 species of this genus which I know of is gregarious in habit ; 

 but usually not more than four or five bodies are to be found 

 attached, like Anthophysa, by their narrower posterior ends, to 

 the branchlets of a single forking stem. The peculiarity in re- 

 gard to the direction of the curvature of the flagella in a back- ' 

 ward direction toward the stem, is as highly marked in Codosiga 

 a's in Anthophysa (described by me in the Number of the 'An- 

 nals' for December, 1866) ; and there is also the same fixed 

 relationship of the longitudinal and the greater and less trans- 

 verse diameters of the several individuals of the colony. 



There is still another new genus which I should like to men- 

 Ann. o; Mag. N. Hist. Ser. 3. Vol. xix. 2 



