PffLEBCEDEStS JN CH&TOPODA 



27 



Astacus and of Limulus, should be regarded as remnants of the 

 coelom, the bulk of which has been filled up by swollen blood- 

 vessels, leaving only epinephric and gonadial sacs in the Arthro- 

 poda, pericardial and gonadial sacs in the Mollusca. 



Some years later my assistant, Dr. Benham, now Professor in 

 Dunedin, New Zealand, described (Quart. Jour. Micr. Sci. xxxix. 

 1896) a condition of the blood-vessels in the Chsetopod Magelona, 

 which is parallel to that through which the vessels of ancestral 

 Molluscs and Arthropods must have passed. Phlebcedesis is carried 



l.ext. 



dor TL m,. 



circ. 





-obi. 



crc. 



FIG. 14. TRANSVERSE SECTION OF THE THORACIC REGION OF THE CH^TTOPOD MAOELONA 



TO SHOW THE SWELLING OF THE BLOOD-VESSELS AND CONSEQUENT REDUCTION OF THE 

 CCELOM. 



D.v, dorsal vessel; G, gut; N, nerve corrl ; F.r, ventral vessel greatly swollen, 

 filled with a peculiar corpusculated blood ; lat.ext, lateral extension of the same ; OB, 

 coelom ; l.v, lateral vessel ; l.m, longitudinal muscles ; circ, circular muscles ; obi, 

 oblique muscles ; dor.v.m, dorso-ventral muscle. (After Benham.) 



to such a point in Magelona as to extinguish to a large extent 

 the proper coelomic cavity (see Fig. 14). This observation seems 

 to be of importance as showing the tendency to Phlebcedesis in 

 Chsetopods among the ancestors of which the ancestors of both 

 Mollusca and Arthropoda are in all probability to be sought. 

 When we remember further that in some Choetopods the cells 

 which should form the blood-vessels and the blood, may actually 

 break up altogether and give rise to floating hsemoglobinous 

 corpuscles with a total absence of blood-vessels (Glycera and 

 Capitellidse), we must admit that it is not surprising that the task 



