28 POPULAR ILLUSTRATIONS OF 



Now let us examine the objects seen through the clear diaphanous 

 substance of the animalcule. First, notice the two clear circular 

 spaces marked a a, Fig. 18 (p. 27). These are termed the contractile 

 chambers or vesicles, which are observed to be continually opening 

 and shutting that is to say, they are alternately visible and 

 invisible. Now these contractile chambers, or vesicles, or spaces, as 

 they have been at different times called, are a marked feature in the 

 structure of the Infusoria. They are observed to be connected with 

 channels having a communication with the outside of the body, 

 through which these chambers are alternately filled with and 

 emptied of water. Kolliker has shown this in a beautiful series 

 of figures in his "Icones Histiologicae," which I have copied 

 (Figs. 20-24). 



Fig. 20. Fig. 21. Fig. 22. Fig. 23. Fig. 24. 



Figs. 20-24 Contractile chamber of Paramsecium in five successive stages (after Kolliker), 

 magnified 500 diameters 20, the chamber or vesicle contracted, and the rays tilled with 

 water 21, the first emptying of the rays and simultaneous filling up of the chamber 

 22, the second filling of the rays 23, the second emptying of the same, and probable 

 filling of the chamber 24, commencement of the emptying of the chamber and after- 

 filling of the rays. 



This water circulation is, no doubt, connected with the process of 

 respiration ; that is to say, it is the means by which oxygen sus- 

 pended in the water is conveyed to the interior of the animalcule, 

 and carbonic acid conveyed away. 



And mark, this beautiful apparatus is one of the types upon which 

 this class of living beings is formed. We shall see by and by, in 

 the higher animals, many different modes of breathing ; but in none 

 shall we find an exact repetition of these contractile chambers and 

 canals. Now let us look at the two bodies marked b and c, Fig. 18 

 (p. 27). These have been named the nucleus (b), and the nucleolus (c). 

 But they do not represent parts equivalent to the nucleus and nucleolus 

 of cells. The body marked b is, in fact, the ovary, and c bears the 

 same relation to it as the pollen grain does to the ovary of the plant, 

 as we shall see by and by. 



At d d notice particles which have been swallowed as food, sur- 

 rounded by globules of clear water, which was probably taken in 

 with the food. These globules were considered by Ehrenberg as 

 so many distinct stomachs, and upon this mistake was founded the 

 order Polygastrica, or " many stomachs." This, as I have already 

 stated, is quite erroneous. At e. and scattered all through the 



