TRANSACTIONS OP THE SECnONS. 65 



be detected. There is no trace of nervous or muscular tissue, and the high degree of 

 contractility presented by the animal, must be an endowment of its simple cellular 

 structure, but whether residing in the membrane of the cells or in their contents, or 

 ia both, we have not yet sufficient facts to enable us to determine. 



On the Structure of Bursaria. 

 By Professor Allman, M.B., M.R.I.A. 

 In this communication the author advocated the unicellular structure of the true 

 Infusoria as maintained by Siebold. The phsenomena presented by Bursaria incon- 

 testably prove it to be a solitary cell with an inversion of its wall at one spot, 

 constituting a deep horn-shaped depression, which terminates behind in a blind 

 extremity. The whole of the external surface of the animalcule is thickly set with 

 vibratile cilia, and within the horn-shaped depression, along the entire of its convex 

 side, there runs a broad band of vibratile organs, which appear to be very delicate 

 plates rather than cilia. 



The contents of the Bursaria-cell are remarkable. Under slight pressure and a 

 magnifying power of about 100 linear, the whole of the interior appears at first to 

 be composed of a cellular parenchyma. It is, however, easy to convince oneself that 

 this appearance of cells is due to the presence of simple vacuolae, thickly distributed 

 through a semi-fluid granular substance. When by rupture of the external wall, 

 a portion of these cell-contents escapes into the drop of fluid in which the animal is 

 placed for observation, it may be seen to possess the property of immediately as- 

 suming a definite outline ; it generally acquires a nearly spherical figure, and with a 

 number of contained vacuolse, it then so exactly resembles a parent cell with second- 

 ary cells in its interior, as to be very likely to give rise to erroneous views of the 

 structure of the animalcule from which it had been liberated. It is not easy to 

 decide whether the masses of escaped cell-contents possess a power of independent 

 motion ; there is reason, however, to believe that such power is really possessed by 

 them, and that it manifests itself in slight changes of shape, which after consider- 

 able intervals may be witnessed in them, and which cannot be referred to any purely 

 mechanical cause. In the unmutilated animal a movement of the contents may 

 be frequently seen through the transparent cell- wall, during which the vacuolae con- 

 stantly change their relative position to one another. 



In the midst of the cell-contents is a sinuously bent cylindrical body of a yellowish 

 colour, and somewhat granular structure ; it is solid, and appears to lie quite free in the 

 surrounding substance. It is to the homologues of this body in so many Infusoria, 

 that Ehrenberg has so variously attributed a digestive or reproductive function, or 

 that he has assigned some undefined glandular office. Siebold, however, has certainly 

 indicated its true signification when he supposed it to represent the nucleus of the 

 unicellular solitary cell, forming the body of every true Infusorial. 



In a well-fed Bursaria, masses of alimentary matter may be seen enclosed in little 

 cavities scattered through the substance of the animalcule. These cavities seem to 

 have no definite position, and there appears to be no doubt whatever that they are 

 mere vacuolse temporarily excavated in the substance of the cell-contents, for the re- 

 ception of the alimentary matter. Their contents, when presenting any definite form, 

 may be seen to consist chiefly of minute Desmidieos or DiatomacecB or Infusoria, but 

 most usually the cavities contain nothing but granular brownish masses. The author 

 '■ had not succeeded in witnessing the actual reception of food, and could not state, 

 from direct observation, how this gained admittance to the interior ; there seems 

 I little doubt, however, that it is first carried into the horn-shaped depression, through 

 I whose walls it is then forced into the interior of the animalcule, and when once in- 

 I troduced into the semi-fluid cell- contents, each little alimentary mass forms around 

 it a vacuole. In this vacuole digestion goes on, and during the continuance of the 

 process each may be seen to contain, besides its solid contents, a transparent colour- 

 \ less fluid. The temporary digestive vacuolse seem capable of formation in any part of 

 ! the cell-contents ; they are the so-called stomachs of the advocates of the polygastric 

 structure of the Infusoria, 



I While engaged in the examination of specimens of Bursaria, it occasionally hap- 

 pened that a minute pyriform body, with a ciliated surface and vacuolated structure, 

 became detached and swam rapidlv away. The definite form of this little locomo* 

 i 1853, ■ S 



