122 



Dr. Cobbold on the Anatomy 0/ Actinia. 



base, the ova or gemmules coming out through this open tubular 

 stomach*." 



That this viscus is assuredly not simply a membranous sac or 

 bag closed at the base, our own inquiries have fairly demon- 

 strated. We were led to this investigation by the following 

 circumstance. Two species of A. mesemb?-i/anthemum'were taken 

 one afternoon last October from the north shore of the Firth of 

 Forth, and on arriving at Edinburgh the same evening, the 

 number (in the vessel) had increased to thirty-five. The animals 

 were therefore cai-efully watched that night, but not until next 

 day were we gratified by witnessing what has been shown by 

 numerous observers to occur, viz. the evolution of the young 

 (of all shapes and sizes) by the mouth. On dissecting one of 

 the adult Actinias, it was found, as we were thus led to anti- 

 cipate, that a considerable opening obtained to the base of the 

 stomach, admitting the tip of the little finger, aud freely com- 

 municating with the interseptal spaces and general abdominal 

 reservoir. This, to our mind, fully cleared up the difficulty so 

 often expressed concerning the passage by which the young 

 polyps gain access to the digestive cavity and are ultimately set 

 free. 



The existence of this opening (which if not functionally may 

 morphologically be regarded as the pylorus) was further rendered 

 evident by a careful examination, aided with low magnifying 

 powers, of the embryo polyps. In the present instance none of 

 the individuals, although extremely small and of various forms, 

 presented the vibratile or ciliated character which the late Sir 

 John Graham Dalyell has shown them to possess in their earliest 

 condition. The smallest were semi-opaque spherical bodies, 

 while the remainder presented every gradation of form, from the 

 simple sphere up to the complete tentaculated polyp. The 

 largest were about the size of peas. On section they presented 

 appearances similar to those ex- 

 hibited in the accompanying 

 diagrams, which are intended 

 to illustrate the manner in which 

 the morphological changes are 

 brought about, and the several 

 special organs unfolded. The 

 figures may be thus explained : 

 — 1. Outline of mature embry- 

 onic corpuscle after the disap- 

 pearance of the cilia. 2, 3, 4. Primary involution of integu- 

 mentary membrane. 5, 6. Re-induplication of external mem- 



* Prof. Goodsir informs me that he has repeatedly pointed out, in his 

 Lectures, " the occurrence of this opening," and has referred to it as typical 

 of the entire group of helianthoid polyps. 



