78 ACALEPIIS IN GENERAL. Part I. 



have an additional cliaracteristic of this Ijranch, distinguishing it from the three 

 other In-anches of the animal kingdom. The significance of this upright position 

 of the lowest type of animals •with a I'adiating structnre is most striking in view 

 of the upright j^osition of man, at the head of the animal creation. 



The same reasons which induce me to discard the indications of the Holothuria^ 

 in determining the normal positioii of the Eadiates, apply to the Medusiv, Star- 

 fishe.s, and Sea-urchins, when considering which end of the vertical axis should be 

 regarded as the upper and which as the lower. The centre of radiation, as 

 developed in the actinostome, is evidently the prominent feature of the whole 

 organization of this t_\pe ; it is the climax of the concentration of their structure; 

 upon that side the most sensitive ^^arts of the Ijody are combined ; around it the 

 nervous ring with its ganglions is placed, in those representatives of the type in 

 which the differentiation of the tissues goes so far as to lead to the development 

 of a nervous system. It seems natural, tlierefore, to consider the oral end of the 

 vertical axis as its upper end. But why that end should be turned upwards in 

 the lower Radiates only, I am unaljle to say : I can only surmise that this position 

 is connected with the immovability of the Polyps, the Ilydroids, and the peduncu- 

 lated Crinoids, and that the advantage they have in that respect over the Medusae, 

 the Star-fishes, and the Sea-urchins, is a compensation for their inability to move 

 about freely. 



Supposing, however, that the actinostome should be considered as the upper end 

 of the vertical axis, it would not be advisable to use the expressions of ^ipj^cr 

 and loivcr end or side of the body, in describing the one or the other end of 

 the vertical axis of the Radiates ; for, evidently, there would be something unnatural 

 in constantly contrasting the normal position and the natural attitude of the differ- 

 ent representatives of this type. I would therefore ^^I'l-'l^'r to apply the name of 

 adinul to the side or pole at which the so-called mouth or actinostome is placed, 

 and that of ahadinal to the opposite side or pole. In this way the description 

 of a Sea-urchin, compared to that of an Actinia, will not involve a, seeming con- 

 tradiction with the attitudes in which these animals are constantly observed in 

 their natural element. 



This once fully understood, and assuming that the Ijody of a Radiate, whatever 

 be its real figure and its natural attitudes, may be reduced to a spheroidal form 

 by homological transformations, it is .?elf-evident that the essential segments com- 

 posing this living sphere will bear to one another identical relations, and as parts 

 of a sijhere jje homologous to one another, as far as they retain symmetrical 

 relations to the main axis. For these homological segments of the body of Radi- 

 ates I would propose the name of Sphemmercs, and, in allusion to the well-known 

 structure of these animals, descriljc the body of a Ilolothuria, for instance, or that 



