16 Prof. Muller on the Anatomy and Development 



old meaning, we know of only one creature which is entitled to 

 the name, viz. the Diplozoon paradoxum, which Von Siebold has 

 just shown to be really formed by the fusion of two previously 

 distinct individuals. 



We hope that the reader will pardon this long digression into 

 the regions of abstract thought. Whether he adopt our view or 

 not, we trust that at any rate, we have pointed out where the real 

 battle of the alternation theory lies. 



The onus of giving a new meaning to the word " individuality 9 * 

 must rest with the advocates of the alternation theory ; we have 

 endeavoured merely to make a consistent extension of the old 

 meaning to embrace new facts. 



The Echinoderms have been included under the " Alternation 

 theory ;" but, if the reasoning above be correct, unjustly, as is 

 indeed plainly pointed out on other grounds by Prof. Muller in 

 his second memoir. He justly observes that the process of de- 

 velopment of the Echinoderm partakes as much of the nature of 

 metamorphosis as of " alternation." The larva and the Echino- 

 derm cannot be said to be two individuals, when they possess 

 the same intestine. 



Nor, as to the question of fact, does the development of the 

 Echinoderm appear to be a case of " Parthenogenesis." 



The structure of the integument of the larva, at the place where 

 the tubular rudiment of the Echinoderm is subsequently formed, 

 is quite undistinguishable from that of any other spot. There 

 are here no descendants of the embryo-cells specially set aside to 

 become developed into the new structure*. 



The development of the Echinoderm is then neither a process 

 of " alternation of generations " nor of " Parthenogenesis," but 

 the individual consists of two zooids — a larva-zooid and an Echi- 

 noderm-zooid, the latter of which is developed from the former 

 by a process of internal gemmation j\ 



* The elongated cellular masses which exist on each side of the digestive 

 canal in the larvae, are very possibly the immediate descendants of the embryo- 

 cells. But Prof. Muller leaves it very doubtful, whether these masses have 

 anything to do with the development of the Echinoderm. Certainly they 

 are not concerned in the development of one most important part of it — the 

 water- vascular system. See Mull. Arch. 1850, p. 466. Ibid. 1851, p. 4. 



t According to Prof. Muller (Archiv, 1851, p. 18) the development of 

 the Echinoderm can only "figuratively" (bildlich) be compared to gem- 

 mation, inasmuch as the " formative mass ** arises independently. 



But since he says immediately afterwards that "the rudiment of the 

 water-vascular system, in general, arises before the rudiment of the parietes 

 of the Echinoderm," and since he shows elsewhere that the origin of the 

 water- vascular system is by the development of a bud-like process inwards 

 — the process may, we think, be called gemmation in much more than a 

 figurative sense. 



