COXTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT 



HARVARD COLLEGE. NO. 282 



THE EFFECTOR SYSTEMS OF ACTINIANS 



G. H. PARKER 



Every animal possesses means, more or less well defined, 

 for responding to environmental changes and in many groups 

 of animals these means are differentiated into definite systems 

 of organs, the effector systems. In any given species the ef- 

 fectors may be independent of, or more or less under the control 

 of, the nervous system. They are obviously often very diverse. 

 In the actinians the most conspicuous of these systems are the 

 mucous system, the nematocyst system, the cihary system, 

 and the muscular system. With each one of these the animal 

 is capable of responding to particular elements in the en\dron- 

 ment and all have been suspected of being in one way or another 

 under nervous influence. The nature of the systems and their 

 relations to the nervous mechanism in the actinians will be 

 taken up in the following pages. 



THE MUCOUS SYSTEM 



Every part of Metridium seems to be able to produce mucus, 

 and, under normal conditions, all the surfaces of this animal 

 are covered with a thin laj^er of shmy secretion. This is pro- 

 duced in all probability by the so-called mucous cells and albu- 

 men cells w^hich have been described by Schneider ('02) in 

 Anemonia as occurring throughout the ectoderm especially 

 in the oesophagus and the mesenteric filaments, and generally, 

 though less abundantly, throughout the entoderm. 



If an expanded Metridium is submerged in fresh water for 

 about fifteen seconds and then returned to sea-water, its whole 

 outer surface and especially that of its tentacles becomes cov- 

 ered with a profuse secretion of mucus thus showing the extreme 

 ease with which this material is produced. When a Metridium 

 has been kept in an aquarium whose water supply is not of the 



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