THE ANNTJLOSE TYPE. 603 



besides relatively few segments and few limbs (sundry of them 

 extremely unlike the rest) we have a vascular system concentrated 

 into a central heart with arteries and a concentrated nervous 

 system, such that the great ganglia in the integrated carapace 

 immensely subordinate the ganglia of the remaining segments; 

 and similarly with the other organs. Now unless it be denied 

 that these highest decapods have been evolved from low types 

 akin to myriapods in composition, it must be admitted that the 

 progress has been from a string of many like segments with 

 similar sets of organs to a group of relatively-few unlike segments 

 with dissimilar sets of organs. If so we cannot rationally deny 

 that the progress has been of this nature up from the lowest 

 annelid, instead of having been, as Prof. Korschelt's hypothesis 

 implies, of opposite nature at the beginning. 



In a preceding passage a clear recognition of the normal 

 course of development occurs. In opposing the view set forth in 

 §§ 205-7 of this work, Prof. Korschelt says : — 



" It seems scarcely favourable to this theory that the degree of inde- 

 pendence which the individual segments present is comparatively slight. 

 The most important organs (nervous system, body musculature, blood-vascu- 

 lar system) show themselves to be single fundaments of the entire body, 

 and are also developed as such even though they also exhibit evidences 

 of metamerism. Even the excretory canals may give up their segmental 

 isolation and become united to one another by means of longitudinal canals." 

 (lb. p. 348.) 



On turning back to § 206, the reader will, I think, demur to the 

 assertion that the independence is " comparatively slight " ; seeing 

 that, as in Ctenodrilus, a single segment sometimes becomes sepa- 

 rate and reproduces other segments to form a new series. Instead 

 of admitting that "the most important organs" "show them- 

 selves to be single fundaments of the entire body," it may be 

 held, contrariwise, that their original independence in each seg- 

 ment is masked only to the degree involved by their cooperation 

 as parts of a compound organism. But chiefly I remark that 

 when it is said that " the excretory canals may give up their seg- 

 mental isolation and become united" by "longitudinal canals," 

 there is a clear confession that the isolation of these organs was 

 original and their union superinduced — an implication that the 

 course of evolution is as I have described it, and at variance with 

 the course of evolution assumed by Prof. Korschelt. 



Yet another incongruity is involved in his interpretation. He 

 writes : — 



" Just as in the consideration of the tape-worm chain we were induced by 

 the comparison with unsegmented forms to refer the entire chain to an 

 unsegmented individual, and, on the other hand, to sec in the proglottis, 

 not a complete individual, but only the abstricted hinder portion of the 

 body of the Cestode, in the same manner, and with much more reason, we 

 adhere to the individuality of the Annelid body." (P. 349.) 



