64 THE POPULAR SCIENCE MONTHLY 



From this general discussion it is quite evident that the cardiac 

 muscles of different animals act in very different ways and that while 

 some, like the heart of Limulus, have a neurogenic beat, others like 

 that of the tunicates have a myogenic beat. 



From this rather lengthy digression we may return to the question 

 raised in the earlier part of this lecture, namely, the possibility of the 

 existence of physiologically independent muscles. This I believe to 

 have been demonstrated in part at least in the sphincter pupillas of the 

 lower and perhaps all vertebrates, and wholly so in the tunicate heart 

 and the embryonic vertebrate heart. The complete freedom of such 

 muscles from nervous control and their dependence on direct stimula- 

 tion for normal action is a repetition of a process that, in my opinion, 

 characterized all primitive muscles such as we now meet with in the 

 sphincters of sponges. Such muscles as these sphincters I believe to 

 represent the original and primitive elements around which the other 

 members of the neuromuscular mechanism, the sense organs and the 

 central nervous organs, subsequently developed. In my opinion then, 

 • effectors in the form of muscles preceded in an evolutionary sense the 

 receptors and adjusters, and formed the centers around which these 

 organs developed later. 



References 



Carlson, A. J. The Nervous Origin of the Heart-beat in Limulus, and the 



Nervous Nature of Coordination or Conduction in the Heart. Amer. Journ. 



Physiol, Vol. 12, pp. 67-74. 1904. 

 Engelmann, T. W. Das Herz. Leipzig, 8vo, 44 pp. 1904. 

 Gaskell, W. H. The Contraction of Cardiac Muscle. In E. A. Schafer, Text- 

 book of Physiology, Vol. 2, pp. 169-227. 1900. 

 Hertel, E. Experimenteller Beitrag zur Kenntnis der Pupillenverengerung 



auf Lichtreize. Graefe's Arch. Ophthalmol., Bd. 65, pp. 107-134. 1907. 

 His, W., Jr. Die Entwickelung des Herznervensystems bei Wirbelthieren. 



Abhandl. Egl. Sachs. Ges. Wiss., mathem.-phys. CI., Bd. 18, pp. 1-64, 



Taf. 1-4. 1891. 

 Howell, W. H. The Cause of the Heart Beat. Journ. Amer. Med. Assoc, 



Vol. 46, pp. 1665-1670. 1906. 

 Hunter, G. W. Notes on the Heart Action of Molgula manhattensis (Verrill). 



Amer. Journ. Physiol., Vol. 10, pp. 1-27. 1903. 

 Kraft. H. Zur Physiologie des Flimmerepithels bei Wirbelthieren. Arch. ges. 



Physiol, Bd. 47, pp. 196-235. 1890. 

 Merejkowsky, C. Etudes sur les eponges de la Mer Blanche. Mem. Acad. 



Imp. 8c, St. Petersbourg, Ser. 7, Tome 26, No. 7, 51 pp., 3 pis. 1878. 

 Schultze, L. S. Untersuchungen ueber den Herzschlag der Salpen. Jena. 



Zeitschr. TSTaturwiss., Bd. 35, pp. 221-328, Taf. 9-11. 1901. 

 Steinach, E. Untersuchungen zur vergleichenden Physiologie der Iris. Arch. 



ges. Physiol, Bd. 52, pp. 495-525. 1892. 

 Vosmaer, G. C. J., and Pekelharing, C. A. Observations on Sponges. Verh. 



Eon. Akad. Wetensch. Amsterdam, Sec. 2, Deel 6, No. 3, 51 pp., 4 pis. 1898. 



