"CHAP. xin. 



stomach, where it is digested. Moreover, if we analyse the cat's 

 tissues we shall find they are almost all nitrogenous, such as muscle, 

 nerve, and blood, whereas plants, though containing protoplasm, yet 

 largely consist of a non-nitrogenous substance termed " cellulose," 

 and contain much starch. But we have to seek for distinctions 

 between the whole world of plants, and the cat considered merely 

 as an animal, and therefore for such distinctions as all other 

 animals share with it. Now the above given distinctions as to 

 motor power, sensitivity, external form, mode of reproduction, 

 manner of feeding, and chemical composition, serve very well to 

 distinguish the bulk of animals from the bulk of plants, but when we 

 come to examine the most lowly organised plants and animals all 

 these distinctions seem to fade away. 



Thus, with respect to motor power, very little difference can be 

 perceived between some of the lowest aquatic animals and plants, 

 both of which may be compared to a detached fragment of the cat's 

 ciliated epithelium, since they consist of a few cells which protrude 

 protoplasmic threads, the lowly organism propelling itself about by 

 the lashings of such threads. Other animals of considerable com- 

 plexity of structure such as some of the Tunicates adhere to rocks, 

 and appear quite motionless, save when touched, and then they 

 eject water from two apertures, thus showing a motor power com- 

 parable with that of the squirting cucumber. But there are animals 

 still more inert, such as the bladder- worms, or hydatids, which lie 

 hidden in the flesh (or other parts) of the animals they infest, and 

 which are little more than small membranous bags enclosing an 

 albuminous fluid. On the other hand, various plants show consider- 

 able motor power, such as the sensitive plant, Yenus's fly-trap, and 

 others. 



The last named organism serves to show us also that a high 

 degree of impressionability may be present in plants, though we 

 have certainly no evidence that any of them possess " feeling." 

 But a multitude of the lowest animals seem to exhibit no more signs 

 of sensibility than do the lowest plants. The hydatids, just referred 

 to, may serve as an extreme instance of such apparent insensibility. 

 Hydatids, however, are creatures in an imperfect stage of their 

 development, the adult stages of which (tape-worms) do give evidence 

 of a power of sensation. So that sensitivity may be potentially 

 present in these hydatids as it is in the cat's ovum, which certainly, 

 itself, gives no evidence of, nor can be supposed to possess, any 

 actual power of feeling. On the other hand, such plant-movements 

 as those referred to, are explicable in an altogether different way 

 from the sensori-motor movements of animals, while we have no 

 ground for attributing to them potential sensibility, since under no 

 conditions does it ever become unequivocally actual. 



As to external form, no distinction can be drawn between some of 

 the lowest algae or fungi on the one hand, and the lowest animals on 

 the other, whilst many zoophytes and some other animals, exhibit 

 the branching mode of growth common in plants ; while some plants, 



