Page:Popular Science Monthly Volume 75.djvu/149

Rh connection with the musculature has been advocated by Claus (1878) and by Chun (1880), but a nervous system without effectors is, as Samassa (1892) and Schaeppi (1904) declare, scarcely conceivable.

The opinion about the origin of nervous and muscular tissues as expressed in these articles is opposed to the various theories stated in the preceding paragraphs in that muscular tissue is regarded as the ancestral tissue and nervous tissue is supposed to have formed secondarily and as a means of bringing muscular tissue into action with greater certainty than direct stimulation would do. According to this view the primitive state of the neuromuscular mechanism is to be seen in such animals as sponges, which possess muscles but no true nervous organs; and the neuromuscular or, better, epithelial-muscular cells of the coelenterates represent these primitive effectors to which have been added a diffuse system of receptors as seen in the sea-anemones or a specialized system as in the jellyfishes. In both instances the receptors and effectors are related through a nervous net.