166 REPORT — 1851. 



physiological balance ; it is a subject which conducts to a new path of in- 

 quiry. The problem of organization in the Echinoderm, Acalephae and 

 Zoophytes, through aid of its suggestive guidance, will soon receive a new 

 solution. 



From the researches of Mr. Newport it appears that the series of lateral 

 respiratory sacculi (sic) already described in the leech and the earth-worm, 

 are also present in lulus. This fact, more than any other, serves to demon- 

 strate a near zoological relationship between this myriapod and the Annelida. 

 In the tendency to segmental repetition in the body, in the history of the deve- 

 lopment of the embryo, and in the character and distribution of the main 

 vascular trunks, the lulidce exhibit a close similarity to the Annelida. As 

 the lulidcB differ from insects in the absence of wings, they no less strikingly 

 differ from the Annelida in the possession of articulateil members. 



The true classification of articulate animals can only be reached through 

 the joint aid of comparative anatomy and embryological metamorphoses. In 

 the latter department Agassiz has done much*. These two methods lead, 

 however, to different results. By the naturalist it has been considered that 

 the presence of a heart in Crustacea entitles this class to the highest place 

 among the Articulata. This arrangement is founded upon the view that all 

 animals should form a natural linear series, disposed in one progressive line 

 according to their successive gradations of structure. The distinction intro- 

 duced by Cuvier of different types, of four distinct plans of structure, has 

 not yet sufficiently penetrated the spirit of those who have followed in his 

 steps. Viewed thus as separate types, it is evident that what might be re- 

 garded as a character of superiority in one group, may not be entitled to 

 such consideration in another; that in each type a separate ruling principle 

 should be recognised, and that these types could not be brought into con- 

 nection with each other unless upon the most general considerations. 



The embryo of the Annelid undergoes few, if any, metamorphoses. It is 

 true that the young are at first almost wholly devoid of appendages ; but the 

 body in no instance suffers those deep transmutations traceable in the growth 

 of the larvae of Insects and Crustacea. A considerable change of outward 

 form is impossible, without some mutation of structure. Embryological 

 metamorphoses accordingly become grounds of comparison and induction in 

 the eye of the systematic zoologist. As the metamorphoses of an embryo by 

 which it is raised to its mature phaise cannot be held, at all events, as retro- 

 grade steps in organization ; it is not difficult to perceive that these ' changes ' 

 from the ovum to the perfect animal may lead to valuable inferences as to 

 the real and final place of the adult animal in the series. Now, since the 

 insect reaches the standard of the annelid in its first metamorphose (the 

 vermiform caterpillar), its ultimate destination, after two further mutations, 

 must place it far above the rank of the worm. It cannot be doubted that a 

 comparison, instituted between the larval conditions of Insects generally and 

 the Annelida, would issue in many interesting discoveries : such compara- 

 tive view has actually led M. Agassiz to see in the naked larvae the proto- 

 types of the non-setigerous or Abranchiate Annelids, — and in those provided 

 with appendages a resemblance to the dorsibranchiateand cephalobranchiate 

 worms. Nor does this distinguished naturalist scruple to descend to parti- 

 culars in this comparison, declaring that the larvae of Simacodes may be 

 viewed as terrestrial representatives of the genus Polyno't ; those of Bomhy- 

 ces as corresponding to the Nereids \ while some among the larvae oi Papilio 

 proper, with their protractile branching appendages upon the neck, remind us 



* " Classification on Embryological Data." Trans, of American Association for the Advance- 

 ment of Science, 1850. 



