528 



E. RAY LANKESTER. 



region in frout of the mouth is no longer formed by tlie 

 primitive prostomiiim or head-lobe^ but one or more seg- 

 ments, originally post-oral, with their appendages have 

 passed in front of the mouth (prosthomeres). At the same 

 time the prostomium and its appendages cease to be recog- 

 nisable as distinct elements of the head. The brain no 

 longer consists solely of the nerve-ganglion mass proper to 

 the prostomial lobe, as in Chfetopoda, but is a composite 

 (syncerebrum) produced by the fusion of this and the nerve- 

 ganglion masses proper to the prosthomeres or segments 

 which pass forwards, whilst their parapodia ( = appendages) 



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Aj [A 



Fig. 1*. — Diagram to show the gradual formation of the Art liropod 

 pericardial blood-sinus and " osliate " heart by the swelling up 

 (phlebocdesis) of the veins entering the dorsal vessel or heart of a 

 Chsetopod-like ancestor. The figure on the left represents the 

 condition in a Chsetopod, that on the right, the condition in an 

 Arthropod; the other two are hypothetical intermediate forms. 

 (After Lankester, 'Quart. Journ. Micr. Sci.,' vol. xxxiv, 1893.) 



become converted into eye-stalks and antenna), or more 

 rarely grasping organs. (3) As in Cha3topoda, coelomic 

 funnels (coelomoducts) may occur right and left as pairs in 

 each ring-like segment or somite of the body, and some of 

 these are in all cases retained as gonoducts and often as 

 renal excretory organs (green glands, coxal. glands of 

 Arachnida — not crural glands, which are epidermal in 

 origin) ; but true nephridia, genetically identical Avith the 

 nephridia of earthworms, do not occur (on the subject of 



