388 THE NERVOUS SYSTEM IN GENERAL, [ch. ii. 



of sensation and motion ; just as tlie medullary pulp of the 

 nervous system alone, of all organs of our body_, is endowed witli 

 that faculty, the muscular machine being an auxiliary hereto. 

 It cannot be correctly objected to these remarks, that insects 

 have a cerebrum, and that a complete nervous system exists 

 even in infusory animalcules, and that it is their minuteness 

 alone which conceals them from our researches, however aided 

 by the microscope, for Haller meets these objections at once 

 with the statement,^ that in the larger insects at least, in tsenise, 

 in sea-nettles, and other zoophytes, the cerebrum could scarcely 

 escape observation, inasmuch as they are large, and their other 

 organs are obvious enough, even without the microscope ; and 

 since we can distinguish nodules or globules in polypes by the 

 microscope, and in others fibrils also, there seems no reason why 

 the cerebrum should not be observed as well. Bohadsch clearly 

 illustrates this in his description of the lernsea,^ an animal six or 

 eight inches long and three in breadth, which has many stomachs, 

 an intestinal canal, sexual organs, a heart, and a circular spinal 

 cord, furnished with many knots or ganglia, from which nerves 

 are sent ofi'to adjoining structures, but no cerebrum. It appears 

 to possess very small eyes, but these probably are not true organs 

 of vision. In this creature, in which so many organs are con- 

 spicuous, and the medulla spinalis itself, the cerebrum would be 

 visible also, if there was anything more than the ganglionated 

 spinal cord. In the fimbria, an animal six inches long, he 

 detected a tubular mouth, oesophagus, stomach, furnished Avith 

 muscular fibres, intestines, uterus, epididymis, but no eyes, or 

 lungs, or heart, no vessels or nerves : he observes, however, that 

 these may have escaped his observation. In the hydra, called 

 by others mentula maris [holothuria] , with a cylindrical body a 

 foot long and an inch broad, he could not detect either heart, 

 cerebrum, or spinal cord, nor any viscus except the oesophagus, 

 intestinal canal, and anus. If then a nervous system can be 

 discovered in much smaller animals, it would not have escaped 

 observation in those of a sufiicient size, if it had existed. 

 Therefore, although nature produces sensation and animal 

 motion in man and many other animals by means of a nervous 

 system, there are nevertheless not a few creatures to which it 



' De Part. Corp. Hum. Fabr., torn, viii, p. 2. 



' De quibusdam Animalibus Marinis. Dresdae, 1761. 



