ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 9()9 



a disappearance may be partially explained by a change in the mode of life, 

 for the creature is able to move about, and has not, therefore, the same need 

 for tentacles as has a fixed form. 



The number of mouths may be supposed to be due to division, and the 

 absence of an oesophagus to each supports this view. The change has had 

 its influence on the internal organization, the septa especially having 

 undergone a fundamental modification. If we suppose that a polyp were 

 to lose its oesoj)hageal tube the sej)ta would project freely into the gastric 

 cavity ; if, further, the primary were to divide into a number of secondary 

 mouths, and the colony were to be greatly elongated, the radial arrangement 

 of the septa would disappear. The free mode of life has not been without its 

 influence ; to produce the definite movements the parieto-basilar muscle has 

 become transverse, and the corresponding septa have become altered into 

 partition-like structures. Thus the radial type of a polyp may be easily 

 converted into the bilateral. 



From the same island of Billiton Dr. Korotneff obtained a new species 

 of Tubularia — T. parasitica — which he found living on a Gorgonian. The 

 head of the polyp had the ordinary structure, and the genital jH-oducts 

 presented nothing remarkable. In endeavouring to settle how the two 

 forms could become as intimately connected as they are, it is necessary 

 to remember that a hollow Gorgonian is not rare, while a one-stemmed 

 Tubularian is a really exceptional case. It must, therefore, be supposed 

 that it is the Tubularian which has undergone an adaptive change which 

 has suited its form to that of the Gorgonian — the latter then was the 

 original host, and the former the parasite. It is possible that an embryo 

 fixed itself either to the end or to the side of a branch of the Gorgonian, 

 and then, if at the end, made its way in by boring, possibly with the aid of 

 an acid, to the internal axial cavity, where it commenced to grow ; in the 

 neighbourhood the mantle of the host would be more feebly coloured, and 

 much fewer polypides would be developed. If the embryo fixed itself to 

 the side there would be no need for it to bore its way in, and the Gorgonia 

 would in time grow over the Tubularian. 



Polyparium ambulans.* — Prof. E. Ehlers has some suggestions as to 

 the characters of Dr. Korotneff's form (see supra). He calls attention to 

 Bicordea florida, in which from single persons there are developed colonies 

 with incomplete division of the several persons. He differs from Korotneff 

 in regarding Polyparium as one person, and he thinks that it has tentacles, 

 but no mouth — the mouth-cones not being mouth-orifices, but tentacles ; 

 the observations of Prof. E. Hertwig on the Actiniaria of the ' Challenger ' 

 would support this view. If this be the right way of looking at the matter, 

 the septa would be found to present no really abnormal characters. The 

 most important question is raised when we come to discuss the phylogenetic 

 origin oi Polyparium, and the suggestion is made that it is a " paranomally " 

 (as opposed to eunomally) developed animal, or one that, owing to the 

 influence of external conditions, has departed from the typical mode of 

 development, comparable to what is seen among fishes in the Lepto- 

 cephalidsB. In fine, Prof. Ehlers is inclined to think that Polyparium 

 ambulans is a mouthless single animal, derived from a unioral Actiniau 

 with wide degenerate tentacles, and that under the conditions of its life it 

 has paranomally developed its band-like form ; it may be able to reproduce 

 itself asexually by fission. But Prof. Ehlers is careful to remark that his 

 suggestions are made after reading Dr. Korotneff's paper only, and not after 

 a personal examination of specimens. 



* Zeitschr. f. Wiss. ZooL, xlv. (1887) pp. 491-8. 



