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cessive detachment of the arms takes place in the normal state as a voluntary act of the 

 animal, conducive to non-sexual propagation (by divisio radialis). 



There is another feature in the species of Brisinga here noticed which is worthy of 

 remark, as essentially supporting the theory above developed; and that is the contrast to 

 the real radiates (Zoophytes), in the great inconstancy of the number of the rays (arms), 

 which even makes it very difficult to decide what number shall be considered as normal or 

 typical. A similar, although certainly not so extensive, inconstancy is found only in some 

 few forms within the group of star-fishes, which we must consider as the oldest and most 

 original Echinoderms. Thus the number of arms varies not a little in our two species of 

 Solaster. as also in several exotic forms of the genus Asterias, Luidia, Ophidiaster. In most 

 of the star-fishes however the number of arms has with the increasing centralisation of the 

 cormus become fixed at the number which is typical for the Echinoderms, namely five. The 

 same is the case with the Ophiurae, which stand next to the star-fishes, where in like man- 

 ner the number five, with very few exceptions (some species of the genera Ophiacantha, 

 Ophiactis and Ophiothela with 6 arms) is completely constant; and in the 2 most divergent 

 groups of Echinoderms, Echinoids and Holothurians, in which the centralisation of the body 

 has attained its highest degree, not a single instance is to be found of deviation from the 

 normal number of five ambulacra. It is also only in these groups that, collaterally with the 

 complete concrescence of the single individuals (persons) originally composing the body, new 

 and peculiar relationships appear, which seem still more to disguise the original polymerous 

 composition. Thus we see in the so-called irregular Echinides (Spatangus) and in divers 

 Holuthuriie (Psolus), that there proceeds from the whole cormus, by means of one of the 

 sides acting as a sort of creeping disc, (the ventral side) an apparently single bilaterally 

 symmetrical individual; and in the footless Holothuriae (Synapta) where proper ambulacrals 

 are wanting, the last remnant of the complex character has disappeared, and the whole 

 body seems even to return to the lowest (monaxonous) fundamental forms. If we consider 

 one of these anomalous forms by itself, it will certainly be difficult to recognise in it any 

 real complex or cormus. But if we go through the whole series of Echinoderms, we shall 

 soon see that there can be no question of any other than phenomena of secondary adaptation; 

 and these abnormal relations can therefore by no means disprove the above noticed theory 

 of the original composition of the body of the Echinoderms, as derived from the oldest and 

 most original forms of star-fishes. 



