GENUS CARCHESIUM. 691 



each separate zooid is able, through the isolation of the muscular fibre of its pedicle, 

 to contract independently of its fellows, it more usually happens that a whole branch, 

 or if much disturbed, the entire colony, as shown at PL XXXVI. Fig. 2, becomes 

 drawn together into a spheroidal mass, the basal portion or main stem in this case 

 assuming a spiral or closely adpressed zigzag contour. It is not to be wondered at 

 that so prominent and widely distributed a species as Carchesium polypinum attracted 

 the notice of the older investigators. It is included as one variety of the " Bell- 

 like animalcule " described by Leeuwenhoek in the ' Philosophical Transactions ' for 

 1703, and receives the respective names of Sertularia polypina and Vorticdla polypina 

 from Linnaeus in the tenth and twelfth editions of his 'Systema Naturae,' A.D. 1758 

 and 1767. Trembley,* again, accepting this type as akin to the fresh-water polype, 

 with which his name is so eminently familiar, bestowed upon it the suggestive title 

 of " Polypes a bouquet." Both Ehrenberg and O. F. Muller report of this species 

 that it is an inhabitant of both salt and fresh water, but the present author is in- 

 duced to think that under the former conditions it has been confounded with the 

 somewhat similar, and more essentially marine type Zoothamnium arbuscula. De 

 Fromentel t represents the internal muscular fibrilla of the branching pedicle in this 

 species as transversely striate and capable of contracting spirally within its outer 

 sheath ; this outer sheath is also delineated by him as exhibiting closely approximated 

 transverse annulations. The somewhat similar interpretation of this structural 

 element submitted by Mr. H. E. Forrest in the ' Midland Naturalist' for April 1879, 

 is reproduced at PL XXXVI. Fig. 6. The author has on numerous occasions sought 

 to corroborate this accredited striated aspect of the central contractile fibrilla as 

 given by various writers in connection with Carchesium and other members of the 

 Vorticellidan family, but in no instance with success. In place of this, as recorded 

 in the preceding description of Vorticdla nebulifera, see p. 674, the central muscular 

 cord was found to be of apparent homogeneous consistence, but enclosed within 

 a separable delicate hyaline membrane, a representation of such structural differen- 

 tiation as observed in Carchesium polypinum being given at Fig. 3 of the accompany- 

 ing woodcut. According to the most recent investigations of T. W. Engelmann,J 

 the posterior or aboral circlet of cilia developed by the migrant zooids of this and 

 other Vorticellidae originates, as shown at PL XXXV. Figs. 30 and 31, from a 

 distinct annular ectoplasmic band, having the appearance, under moderate magnifi- 

 cation, of being simply obliquely striate, but which under more minute analysis is 

 resolved into closely approximated rows of granules upon which the cilia are 

 elevated. A diagrammatic outline of the oral and peristomal elements of the present 

 species, typifying likewise the same structures as common to all representatives of 

 the Vorticellidae, as given by Green*", is reproduced at PL XXXV. Fig. 51. 



Carchesium spectabile, Ehr. PL. XXXVI. FIG. 26. 



Bodies broadly and evenly campanulate, dilated anteriorly, subspheroidal 

 when contracted ; zoodendrium two lines in height, forming an obliquely 

 conical, or irregularly branching bush. HAB. Fresh water. 



The original illustration of this species, as given by R6sel, is herewith repro- 

 duced. The form next described, referred with doubt to this type by Claparede 

 and Lachmann, is regarded by the author as possessing sound claims for separate 

 specific recognition. 



Carchesium Lachmanni, S. K. PL. XXXVI. FIG. 21. 



Bodies elongate-conical or thimble-shaped, truncate and not dilated 

 anteriorly, pyriform and plicate 'anteriorly when contracted ;/ cuticular sur- 

 face finely striate transversely ; endoplast curved, longitudinally disposed, 



* 'Phil. Trans.,' 1744. t ' Microzoaires,' 1876. 



\ Pfliiger's ' Archiv Physiol.,' Bd. xxiii., 1880. ' Insectenbelustigungen,' 1755. 



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