280 M. straus-durckheim's 



comprising the Parasita, which constitute a separate order, 

 containing Nymjihon, Phoxichilus, Pycnogoniim, Cyamus, 

 Cecrops, Call g us, Dichelestion, Chondracantha, and Lerncea, 

 are followed by the Amphipoda, the Stomapoda, the Deca- 

 poda, and Limulus, which genus forms a separate order, under 

 the name Gnathapoda, conducting us to the pulmonary Arach- 

 nida. The Decapoda lead, on the one hand, to the Ostropoda, 

 and, on the other, to the Branch'iopoda and Cirrhopoda. 



The distance is certainly considerable between the Myria- 

 poda and the dorsibranchial Annelida ; but perhaps a few 

 links only are wanting to connect the last to the only family of 

 Annulosa with solid external teguments, to which they bear 

 any relation. Probably, if any species be found to fill this 

 void, they will also establish a less abrupt passage from the 

 last Amielida to the isopodous Crustacea. 



The transition from the Myriapoda to Lepisma is also 

 rather sudden, but their affinity is evident ; that from Lepisma 

 and Podura to Forjicula is very natural, the Thysanura being, 

 as it were, wingless Coleoptera : the genera Ricimts and 

 Pediculus form a lateral branch of the Thysanura. 



The opinion already noticed, that the Annulosa are more 

 nearly connected with the Veriehrata than are the Mollusca, 

 and consequently form the second great division of the animal 

 kingdom, is true with regard to the modes of organization 

 according to which these three divisions are formed, and also 

 corresponds with the degree in which their faculties are 

 developed. The Vertebrata are characterized by an articu- 

 lated body, of which the two lateral halves are symmetrical, 

 sustained by an internal skeleton, the central portion of which 

 is composed of a series of parts, to which the other parts of 

 the skeleton are attached. 



In the Annulosa, the symmetry of the two sides of the body 

 is still greater than in the Vertebrata ; the body is likewise 

 articulated, and formed by a series of central parts, to which 

 the others are attached ; but they have no internal skeleton. 

 In both, the nervous system consists principally of a spinal 

 marrow, from which arise most of the nerves of the body ; but 

 there is this difference in the Vertebrata, the spinal marrow is 

 dorsal ; in the Annulosa, ventral. The muscular system is as 

 fully developed in the Annulosa as in the Vertebrata ; the 

 muscles offer nearly the same form, and are as perfectly distinct. 



