. The elementary nervous system . 118 THE ELEMENTARY NERVOUS SYSTEM papers will find it by no means easy to separate in them fact from speculation and, consequently, it is difficult to state in exact terms Apathy's real contribution to this subject; but, however this may be, it is certainly true that the appearance of his publications excited others to a further investigation of the subject with the result that nerve-nets were proved to exist in a number of animals. As already stated, they were definitely identified by Bethe (1903) in jellyfishes, by Wolff (1904) and by Hadzi (1909) in hydro-
. The elementary nervous system . 118 THE ELEMENTARY NERVOUS SYSTEM papers will find it by no means easy to separate in them fact from speculation and, consequently, it is difficult to state in exact terms Apathy's real contribution to this subject; but, however this may be, it is certainly true that the appearance of his publications excited others to a further investigation of the subject with the result that nerve-nets were proved to exist in a number of animals. As already stated, they were definitely identified by Bethe (1903) in jellyfishes, by Wolff (1904) and by Hadzi (1909) in hydro- zoans, and by Groselj (1909) in sea-anemones. In fact, the coelenterate nerv- Fio. 36.—Nerve network from a small j i blood-vessel in the .palate of the frog. OUS System Seemed LO DC (After Prentiss,.1904.) ., . ' , nothing but a nerve-net. Evidence was soon brought together to show that nerve-nets were at least components of the nervous sys- tems of echinoderms, worms, arthropods, molluscs, and even vertebrates, where they were especially asso- ciated with the digestive tract and the circulatory sys- tem (Fig. 36), including the heart. Thus nerve-nets were identified from the ccelenterates to the vertebrates, and some of the more ardent advocates of this type of nervous organization went so far as to assume that it was the only type of nervous structure really extant and that the evidence of a synaptic system rested upon his- tological artefacts that obscured the real relations of cell to cell. But this extreme position has not been justified by further research. It is now generally admitted that the conceptions of a synaptic system and of a nerve-net are not opposing ideas, but represent two types of nerv-
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