OF THE PROTOZOA. CILIATA. 321 



cimens of ChiUdon CucuUulus, to one or other or to both of the conditions we 

 have mentioned, than to the purely hypothetical notion of the presence of a 

 state of " over-ii-ritability " in a presumed vascular network. It is here 

 worth calling to mind Stein's belief that gentle pressure may give rise to a 

 stellate or branched appearance of the vesicle, and that the conflicting ac- 

 counts between Ehrenberg and Focke are reconcileable on the supposition 

 of this occurrence (Stein, p. 240). 



With reference to the hypothesis that the vascular apparatus is only ex- 

 cretory in function, we may remark that the exercise of such an office is no 

 bar to that of a respiratory function, since the latter is in itself in part an 

 excretoiy process, and among the lower Invertebrata many examples might 

 be cited where one and the same mechanism is equally respiratory and ex- 

 cretoiy in purpose. 



We may add that Mr. Samuelson (J. M. S. 1857, p. 105) agrees with 

 Lachmann in attributing to the contractile vesicle a cardiac nature, and sup- 

 phes the following particulars: — "In Paramecium caudatum a species of 

 Amphileptus, a freed Vorticella, &c., I have frequently and clearly traced 

 the canals that empty themselves into the contractile vesicle. In the second- 

 named species these canals were very perceptible ; they proceeded along the 

 edge of the body where the cilia were the most active (also probably because 

 there the ciuTent of fresh water would be constantly renewed), and, at the 

 embouchure into the central vesicle, swelled into a biilb-shape. In the Vor- 

 ticella, the cordractile vesicle had a canal which either communicated with the 

 external surface through the oral aperture, or passed round the oral wreath. 

 I was inclined to beheve the latter to be the case (perhaps my bias may have 

 influenced the observation). 



" In certarcL Infusoria there appears to be a more active vital power than 



in others. Thus in Glaucoma (especially such as are probably lai-val 



forms), the contractile vesicle appears to have the power only to form a row 

 of auxiliary vesicles around it, whilst in Ami^hileptus (which approaches the 

 Planaiians in its character), the Setifera or bristle-bearers, and other types 

 it is more powerful, and the fluid is ejected with sufficient force to work its 

 way into the body, and form canals or arteries, however primitive they may 

 be. The progressive vitality I have often noticed in the same form at dif- 

 ferent stages of its growth." 



On a survey of the facts and opinions now passed in review, it seems to us 

 that the contractile vesicle is a closed sac representing a central circulatory 

 organ or heart in its most rudimentary condition ; that this cardiac sac pro- 

 pels its contents through a more or less complex system of channels, probably 

 walled, extended through the cortical lamina of the body ; that the contents 

 represent a chyle or blood, formed by the process of digestion, and absorbed 

 by the vessels ; that this chyle is exposed in the cardiac pulsating vesicle 

 especially, and in the ramified channels less, to the indirect action of the water 

 incessantly introduced withia the body, or constantly surrounding it exter- 

 nally, and thereby becomes aerated, and consequently in all probability fur- 

 ther elaborated; lastly, that the perfected chyle is circulated through its 

 channels, and brought by them into the immediate vicinity of the tissue in 

 which the most active vital changes are going on, and which, on account of 

 its higher differentiation, especially when in the form of cilia, integument, 

 &c., demands the greatest supply of nutritive matters to repair its waste and 

 to provide for the processes of growth and development perpetually proceed- 

 ing in it or in its appended organs. 



Since the foregoing review of the structure and fimctions of the contractile 

 vesicle was written, Lieberkiihn's valuable contribution, founded on original 



