322 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Actiniaria and the Protanthea, and is only a further development of this 

 muscle. 



Morphology of Coral Polyps.* — J. E. Duerden sums up his con- 

 clusions as to the relationships of Madreporarian corals. With the 

 exception of the characteristics dependent on the presence of a skeleton, 

 the Madreporaria present no feature which separates them from ordinary 

 hexameral Actinians. The development and arrangement of the 

 mesenteries and the tentacles in both the protocnemic and metaenemic 

 stages are the same in both groups. In the absence of siphonoglyphs 

 from the stoniodaeuni, and of lateral ciliated bands from the mesenterial 

 filaments, coral polyps differ from the great majority of anemones, but 

 some of the lower Actinians are without siphonoglyphs, and have but 

 simple filaments. 



Modern Actiniaria (excluding the Cerianthege and Zoanthea?) and 

 Madreporaria constitute a single group, one section of which forms a 

 skeleton which is absent in the other. 



On the other hand, the Palaeozoic rugose corals diverge from modern 

 corals after the formation of the six primary septa ; their septa are then 

 added in the same sequence as are the mesenteries in the Zoantheai ; 

 further, the single ventral siphonoglyph of the Zoanthids was probably 

 present in the rugose polyp, being now represented on the skeleton by 

 the " fossula." The Rugosa and Zoanthere undoubtedly constitute a 

 •common group of skeleton-forming and skeletonless polyps, just as do 

 the modern Madreporaria and ordinary hexamerous Actiniaria. 



Protozoa. 



Behaviour of Lower Organisms.! — H. S. Jennings has published 

 an important series of investigations on the reactions of Protozoa, 

 Planaria, and Rotifera to heat, light, and other stimuli. Seven memoirs 

 are included in the volume. The theory of tropisms, the consideration 

 of physiological states as determining factors in the behaviour of these 

 organisms, and the method of trial and error in their behaviour, are 

 subjects discussed on the basis of the experimental data. One or two 

 conclusions only can be quoted. The author decides that the theory of 

 tropisms does not go far in helping us to understand the behaviour in 

 question ; on the contrary, it is when accurately studied as a rule 

 inconsistent with its fundamental assumptions. IwStentor and Planaria 

 it is proved that to the same stimuli, under the same external con- 

 ditions, the same individuals react at different times in radically dif- 

 ferent ways, showing the existence of different physiological states 

 which determine the nature of the reaction. The behaviour of the 

 lower organisms is flexible, by the method of trial and error. This 

 method involves many of the fundamental qualities seen in higher 

 animals, yet with the simplest possible basis in ways of action ; a great 

 portion of the behaviour consisting often of but one or two definite 

 movements — movements that are stereotyped when considered by them- 

 selves, but not stereotyped in their relation to the environment. This 



* Smithsonian Misc. Collections, xlvii. (1904) pp. 9S-111 (16 figs.). 



f Publications of Carnegie Institute, Washington, No. 16 (1901) pp. 1-256. 



