RELATIONS OF ANIMALS. 237 



if I were trying to prove their identity; and in this way I shall 

 be able to make the closest comparison possible. For the sake 

 of conformity to my previous method of procedure, I begin with 

 the lowest types, and from them rise to the higher forms. 



Protozoa and Zoophyta. The first on my list is the alleged 

 transition from the Protozoa to Zoophyta. Among Protozoa 

 the Vorticellce (Epistylis, p. 161, fig. 95) are those which have 

 the closest resemblance to Zoophyta ; and among Zoophyta, 

 Hydra (p. 55, fig. 27) most resembles Vorticellse. Let us place 

 these two forms side by side and try to find what are their points 

 of relationship, if they have any. This can be most easily ac- 

 complished by recurring to the descriptions which I have already 

 given of their internal structure. The Epistylis, or " Bell-ani- 

 malcule," as I have shown, (p. 161, fig. 95,) possesses an oblique 

 mouth, (m,} a spiral gullet, (g-, g- 1 .) a one-sided digestive cavity, 

 (m to 5,) a peculiar pulsating sac, or contractile vesicle, (cv,) 

 and an internal organ of reproduction (ri). On the other hand, 

 I have described (p. 55, fig. 27) Hydra as a simple sac or tube 

 whose mouth opens directly into a wide digestive cavity, (s,) 

 which occupies the whole length and breadth of the body, to 

 the exclusion of any other organ whatever. 



The Epistylis has a type of organization which unmistakably 

 allies it with such animals as Zoothamnium, (p. 175, fig. 104,) 

 Stentor, (p. 62, fig. 30,) Paramecium, (p. 163, fig. 96,) Pleuronema, 

 (p. 170, fig. 99,) Dysteria, (p. 171, fig. 100,) &c., all of which are 

 connected in a common type by their spiral contour, oblique 

 mouth, one-sided digestive cavity, contractile vesicle, and a pe- 

 culiar, internal, reproductive organ. There are certain of the 

 Protozoa which would appear to be an exception to the typical 

 oblique form ; such an one is represented in this figure (Podoph- 

 rya, p. 51, fig. 25). It is an irregular, four-sided, inverted pyra- 

 mid, whose apex rests upon a stalk, and whose four corners are 

 occupied by a group of feelers (/) ; and within are the charac- 

 teristic contractile vesicle (cv) and reproductive organ (/*). This 

 is its conformation in its adult stage, when, as is frequently the 

 case with many other animals, it assumes a disguised shape, and 



