LINNEAN SOCIETV OF LOXDON. XXV 



true body-cavity, or a body and intestinal cavity combined. I had 

 myself" long entertained the generally accepted opinion that the 

 cavity of the Coelenterata represents a body-cavity. I must, how- 

 ever, now give my adhesion to the doctrine here advocated by 

 Haeckel, and regard the pro{)er body-cavity of the higher animals 

 as having no representative in the Coelenterata. I beheve that this 

 is supported both by the facts of development and by the structure 

 of the mature animal. Indeed the body-cavity first shows itself, as 

 Haeckel has pointed out, in the higher worms, and is thence carried 

 into the higher groups of the animal kingdom. 



If such be the real nature of a true intestinal cavity and of a true 

 body-cavity, it is plain that neither the one nor the other can exist 

 in the Infusoria ; for there is here nothing which can be compared 

 with either the endoderm or the ectoderm. 



The whole, then, of the alleged chyme of the Infusoria is nothing 

 more than the internal soft protoplasm of the body. It is quite the 

 same as in Amoeba and many other unicellular animals. 



The peculiar currents which have been long noticed in the endo- 

 plasm of many Infusoria must be placed in the same category with 

 the rotation of the protoplasm observed in many organic cells. Von 

 Siebold, indeed, had already compared the eudoplasm-currents of 

 the Infusoria to the well-known rotation of the protoplasm in the 

 cells of Chara. 



The presence of a mouth and anal orifice in the ciliate Infusoria has 

 been urged as an argument against the unicellular nature of these 

 organisms. The so-called mouth and anus, however, admit of a 

 comparison, not in a morphological, but only in a physiological 

 sense, with the mouth and anus of higher animals. They are 

 simple lacunae in the firm exoplasm, and have, according to Haeckel, 

 no higher morphological value than the " pore-canals" in the walls 

 of many animal- and plant-cells, or the micropyle in that of many 

 egg-cells. KoUiker had already compared them to the excretory 

 canal of unicellular glands. Since, therefore, they do not admit of 

 a comparison with the orifices of the same name in the higher 

 animals, Haeckel proposes for them the terms " Cytostoma " and 

 " Cytopyge" 



So also the presence of a contractile vesicle and of other vacuoles 

 affords no solid argument against the unicellularity of the Infusoria. 

 The physiological significance of the contractile vesicles has been 

 variously interpreted. According to Haeckel, however, these little 

 cavities combine two different functions of nutrition — namely, respi- 



