NERVOUS ACTIONS IN THE VERTEBRATA. 329 



tile dilatations of the larger bloodvessels, at the sides of the branchial appa- 

 ratus. The nervous system which we have here chiefly to consider is com- 

 posed of a spinal cord lying in a spinal canal, above a soft central axis or 

 column, composed of numerous thin discs arranged longitudinally, and form- 

 ing a true chorda dorsalis, or notochord. This establishes the vertebrate char- 

 acter of this singular animal. The spinal cord extends along the whole length 

 of the chorda dorsalis ; it is thickest in the middle third, pointed behind, and 

 presents anteriorly only a slight bulbous cephalic enlargement, but no distinc- 

 tion of parts, like corpora striata, optic thalami, or corpora quadrigemina, much 

 less a separate cerebellum, or cerebrum, and, so far as is known, no folding 

 over of nervous substance, to form a cavity or ventricle. From the sides of 

 the cord, about fifty-live or sixty pairs of nerves are given off', not by double 

 but by single roots. The first pair of nerves, exceedingly minute, supply the 

 membranous parts of the mouth. The second pair give off" long dorsal and 

 ventral branches, which run backwards nearly the whole length of the body, 

 joining the extremities of the anterior and posterior branches of the other 

 spinal nerves. There are no distinct olfactory nerves, but there exists a me- 

 dian concave ciliated spot, in close connection with the fore part of the cephalic 

 bulbous enlargement, which is believed to be the organ of smell ; the optic 

 nerves are represented only by two short processes, at the end of which is 

 some pigment and a transparent body, thus forming two simple eye-spots ; no 

 auditory apparatus or nerve has been detected. The first pair of nerves, just 

 now mentioned, have been considered functionally to represent the fifth cranial, 

 and the second pair the pneumogastric nerve. The spinal cord consists almost 

 entirely of nerve-cells of a spherical form ; they are disposed in a linear manner 

 in the middle third of the cord, but elsewhere, they have an irregular and per- 

 haps segmented arrangement; pigment exists in some of these cells. The 

 white nerve-fibres are indistinctly tubular. No trace of a sympathetic system 

 has been yet described in the Amphioxus. Had not so simple a form of the 

 vertebrate cerebro-spinal nervous system been actually seen, it would have 

 been difficult to suppose its existence. One is naturally tempted to compare 

 it with the nervous system of animals still lower in the scale, especially with 

 that of the Annulosa. But the homologies between it and them are not easily 

 traceable ; however simplified, the fundamental plan of its construction follows 

 a different type ; the oesophagus does not perforate its anterior portion, and a 

 chorda dorsalis runs between it and the perivisceral or body cavity. This 

 singular animal is not a connecting link between the Vertebrate and the An- 

 nulose types. By some, it is considered possible, that it is an embryo condi- 

 tion of a higher form of fish ; and, until its development and subsequent life 

 have been investigated, it may be permitted to doubt the specific character of 

 this highly interesting and apparently archetypal animal. 



On examining physiologically the actions of animals lower in the scale than 

 the Vertebrata, the proper psychical faculties entirely disappear, as well as 

 the distinct cerebro-spinal form of the nervous system. The anatomical ar- 

 rangements of the nervous system, in the several lower subkingdoms, are 

 fiven in the chapter on the general characters of those subkingdoms (pp. 108- 

 12). In even the highest of these non-vertebrate creatures, as in the higher 

 Mollusca and Annulosa, the cerebral hemispheres, properly so-called, are prob- 

 ably no longer represented, although the cephalic ganglia of these animals are 

 frequently designated cerebral. In all the non-vertebrate forms of animal life, 

 intelligence, emotion, and even ideation are wanting ; a feeble perception, and 

 volition, may exist in some of the so-called social insects, viz., in the wasps, 

 bees, and ants ; but sensation is their great guiding principle. The so-called 

 Instincts, which are really the outward expression of sensori-motor impulses ex- 

 cited within their nervous apparatus, assume the control of all their acts, even 

 when these, as in the case of the social insects, seem to us to be adapted to 

 new or unusual conditions of existence. Intelligent acts, characterized by 

 improvability through experience, by the varying adaptation of means to ends 

 under altered conditions, and by the use of different means, to accomplish at 

 will the same ends, are now replaced by instinctive acts, exhibiting a same- 

 ness in all individuals of the same species, at all ages, and under the same 



