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PROCEEDINGS OF THE AMERICAN ACADEMY. 



tive endoderm cells of the zoiiids to every portion of the colony." The 

 system, therefore, in the opinion of the writer, " must be regarded as 

 a nutritive as well as a sensitive plexus." More recently Kassianow 

 (: 08) has demonstrated in xilcjjonium d'tgitatum a well-developed ecto- 

 dermal nervous system with ganglion and sense cells. He denies a 

 nervous function to the branched cells of the mesogloea. 



Returning to the histological structure of Isophyllia, it can be said 

 that the so-called "connective-tissue cells" which bridge the meso- 

 gloea from ectodermal receptors to endodermal effectors fulfill, topo- 

 graphically at least, the requirements of a primitive correlating segment 

 in a reflex mechanism. The ontogenetic history of these cells, and 

 their exact structural interrelations, have not been worked out, so far 

 as I am aware. But the alluring theory presents itself that these 

 branching cells have migrated from the ectoderm, and, spreading 

 throughout the mesogloea, have assumed contact relations one with 

 another by means of their processes ; and though they may not have 

 become highly specialized nervous elements, we may suppose that their 

 protoplasm has retained and augmented its primitive endowment of 

 irritability. Possibly other primitive amoeboid characters have also 

 been retained, such as the capacity for ingesting food, or for moving 

 about by means of pseudopods, — • both of which are suggested by 

 Pratt's observations on the cells of the mesogloeal plexus of Alcy- 

 onaria. 



The theory of the phylogenetic origin of the nervous system as 

 outlined by Parker (: 10), calls for the appearance of an adjustor tissue 

 made up of primitive synaptic neurones as the next step in the process 

 after the development of a sub-ectodermal nervous network, such as 

 occurs in sea-anemones. Future studies, especially those of a histo- 

 genetic character, may reveal that this condition is realized in the 

 loose aggregation of branching cells found in the mesogloea of coral 

 polyps. 



SUMMAKY. 



1. When the rose-coral polyp is stimulated by the application of 

 concentrated meat extract to the oral disk, the latter is drawn down- 

 ward by the contraction of the retractor muscles of the mesenteries, 

 and the margin of the oral surface is folded inward over the disk by 

 the action of a well-developed sphincter muscle. 



2. Meanwhile the stomodaeum is everted, and the mesenterial fila- 

 ments are extruded both through the mouth and through temporary 

 apertures in the oral disk. 



3. The tentacles react quickly to contact stimulation, and affix the 

 object which touches them to their knob-like distal ends, which are 



