EECEXT WOEKS ON THE ENTOZOA. 829 



chain, or median series of centres, comparable to the ventral chain so 

 conspicuous in the type Arthropoda. In the other worms (Fleuro- 

 neura) the nervous centres never present this aspect, but vary much 

 in their arrangement. Often they are reduced, and sometimes 

 altogether wanting. 



On very similar grounds, Mr. Busk, in his Lectures at the 

 Eoyal College of Surgeons, suggested the propriety of placing the 

 higher worms in a province by themselves, intermediate between the 

 Arthropoda and Anmdoida. For the Intestina of Cuvier, as modified 

 by recent researches, he proposed the better name of Scolecida, 



Both the Gephyrea and Botifera are by some arranged 

 with the Scolecida^ by others placed in specially constituted 

 classes. We think Vogt rightly estimated their systematic value 

 when he regarded the former as an order of Annelids, and the 

 Motifera as a separate class. The Botifera have undoubted affinities 

 with the Turhellaria and JPlatyelmia^ whether we consider tiieir 

 nervous or water-vascular systems. But their similarity to the 

 larval conditions of various Polychceta and Gepliyrea is equally 

 striking. On the supposed resemblances of the Botifera to such 

 widely different groups as the Polyzoa and Crustacea we say nothing.* 

 Nevertheless these resemblances, taken in conjunction with the 

 deeper ones already indicated, do, so far as they go, justify the 

 opinion that the Botifera constitute a distinct class of animals. This 

 class clearly belongs to the Anmdoida. 



Lastly, the Scolecida are related, it may be distantly, to the 

 Echinodermata. First, the nervous system of the Echinoderms is 

 more like that of the Bleuroneiira than of the Annelida. Secondly, 

 the water-vascular system of the one class reminds us strongly of 

 the ambulacral vascular system of the other. Again, certain members 

 of both classes present, in the course of their development, a curious 

 combination of metamorphosis with internal gemmation, not wit- 

 nessed elsewhere in the animal kingdom. 



The near affinity of the Echinoderms and Scolecida, and the 

 desirability of uniting both classes into one group, Annuloida, has 

 been urged, for years past, by Mr. Huxley. A more usual view, 

 however, for those who separate them from the Badiata, is to look 

 upon the Echinoderms as equivalent to a primary division, or sub- 

 kingdom. One or other of these two conflicting opinions must be 



* Ley dig and R. Leuckart are the two well-known advocates of these extremes 

 of opinion. 



