62 



LUCERNARIyE AND THEIR ALLIES. 



Structure ; unless we hold tlie pigmental interstitial matter in that category, and 

 even that is most abunchuit in the regions farthest removed from the centre of 

 action, where it is supposed to be in greatest demand. 



124. liatiJc.—ln regard to tlie rank of the Lucernarise, as affected by the con- 

 formation of tlie digestive system, the first thought would be to consider it as 

 indicative of a low grade, because of its apparent diifuseness and want of subdivision 

 into the central cavity and chymiferous tubes, as in tlie majority of the members of 

 the other orders. There may be some truth in this, but it probably does not affect 

 their status to such an extent as might be supposed. AVe have spoken of this 

 diffuseness as airparent, and so we would seem to be warranted in doing if ve 

 assume certain features in the other orders as criteria, ; for instance the digestive 

 system of the higliest of the Strobiloida, viz., Rhizostoma, Cyanea, and their 

 immediate allies. We do not think that the Lucernarine should be compared with 

 the incipient cpUyrarstwje of the Strobiloida, because the latter happens to have 

 broad pouch-like cameras. There is a similarity but not a homology in their forms; 

 but the latter becomes a reality, as far as tlieir different ordinal relations will allow, 

 when the circular tube is developed in the ephyra. But when that takes place the 

 young creature is then on the way to a higlier status, and that very process of 

 going upward is one in which the digestive chambers are becoming more diffuse, less 

 circumscribed, and tending to run all into one broad-spread cavity. This is the 

 condition of things in the Rluzostom'uhe, and Cyaneai, while in the confessedly 

 lower ranks of AarrJice and Pelagice the diffuseness is least. 



125. liilrograde Metamorphosis.— Vc\h\\\)i^ all this may be explained on the score 

 of a partial, digestive retrograde metamorphosis ; and if so, it must be a tendency 

 to a reversion to the simplicity of the Scyphostoma. But we are not willing to 

 admit the verity of that commonly received phenomenon. So far from being a 

 rdro<jra<h; metamorphosis, we doubt very much if any case of the kind that ever 

 came to liand was either more or less than a mere mimetism. This is our theory 

 of the so-called retrograde metamorphosis. In every case which we have examined 

 we found that the organization, instead of retracing its steps, actually took long 

 strides forward. The nervous system of Cirripeilia is a notable instance. The 

 nervous system also of the Acaridean LingtiatuJa is in advance of the same in its 

 normally shaped colleagues; its vermiform outlines do not bear out tlie idea of the 

 correspondence of form' to internal structure. Tlie so-called retrograde meta- 

 morphosis of the feet of the Loggerhead, and other marine turtles, from their 

 embryonic, short, stumped, terrestrial form to the elongate, fin-like flapper, Avith 

 completely inclosed digits, is a mere disguise ; and curiously enough a mimetism 

 of the limb of a higher type, a Cetacean, while it actually surpasses it in point of 

 structural development ; in fact retaining the principal elements of the limbs of its 

 terrestrial congeners, the apimrent retrocession being simply an external feature 

 resulting from a mere elongation of the bones, and their adaptation by conjoined, 

 consentaneous action to another kind of locomotion. And so we might go on with 

 innumerable instances, but we have ventured to digress only far enough to illustrate 

 our views in regard to tlie apparent inferiority of the digestive system of Lttcernaria':, 

 and do not wish to make an entire treatise upon the subject. If there is anytliing 



