166 Mr Matthai, On Reactions to Stimuli in Corals 



entangle food-particles. Shortly afterwards, the oral apertures were 

 widely distended to let in the meat-juice but the process was un- 

 accompanied by eversion of stomodsea. Similar events were observed 

 in Manicina aj-eolata (Linn.). 



When finely powdered carmine was scattered in sea-water con- 

 taining a colony of Manicina areolata (Linn.), it was partly taken 

 into the stomoda^a, the oral lips becoming conspicuously stained. 

 The carmine was, however, subsequently passed out of the stomodaea, 

 showing thereby, that the mouth openings could function as in- 

 halent and exhalent apertures. 



When a tentacle of any of the Astraiid colonies was touched 

 with a fine glass needle, it was suddenly withdrawn in a manner 

 resembling pseudopodial movement and the neighbouring tentacles 

 were also retracted. In Porites and Madracis, whose soft parts are 

 composed of small polyps, the instantaneous contraction of a polyp 

 due to mechanical stimulation caused the contraction of its neigh- 

 bours as well. In all these cases, the wave of contraction started 

 from a centre, viz., the point of stimulation, but remained local and 

 did not spread over the entire colony. 



Series of movements such as the above, made in response to 

 chemical and tactile stimuli, are reminiscent of amoeboid or stream- 

 ing movement of protoplasm, the soft parts of the colonies appearing 

 to serve as the medium for the transmission of stimuli*. If the 

 initial stimulus be too strong, the sudden contraction of the soft 

 parts, due to the mechanical impact, is followed by slow purposive 

 movements. 



The amoeboid character of the movements of the soft parts of 

 Astrseid Corals is in conformity with their histological structure 

 which, on examination, revealed neither a muscular nor a nervous 

 system, although a neuro-muscular apparatus has been supposed 

 by most authors to exist in Madreporaria. The so-called muscular 

 fibres at the base of the ectoderm and endoderm seem to be of the 

 nature of specialised connective tissue fibres, for in both teased 

 preparations and in sections of 4/z — 10/i thicknesses these are found 

 to be without nuclei and to form part of the middle lamina (= meso- 

 glsea) which is itself composed of fine fibres cemented together by 

 a homogeneous matrix containing a few scattered nucleated cells. 

 Fibrils pass into the middle lamina through the granular stratum 

 present at the base of the ectoderm (and less frequently at the base 

 of the endoderm), but these fibrils do not show any histological 

 differentiation which would justify us in regarding them as belong- 

 ing to nerve elements f. 



* Carpenter I'egarded the feeding reactions of Isophyllia as muscular in nature 

 and as brought about by the transmission of impulses of a " nervoid character," 

 but he had not investigated the histological structure of its soft parts {vide Con- 

 tributions Bermuda Biol. Station, No. 20, Cambridge, Mass., U.S.A., p. 149, 1910). 



t For a detailed account of the minute structure of coral polyps vide "The 

 Histology of tlie Soft Parts of Astraeid Corals " to be published shorth'. 



