ON DEVELOPMENT ETC. OF PHORONIS. ôoO 



fact th;it some profound elianges in tlic iir»ani;cinent of the hody- 

 ravities must occui' during the metamorpliosis. As is ac- 

 knowledged l)y all, the suprasepttd cavity of Phoronis is greatly 

 reduced in size as compared with that of the larva, and contains 

 almost no organ except the blood vessels. Tlie infraseptal cavity 

 is, on the contrary, very wide, and contains many important 

 organs, e. //., the alimentary canal, the sexual organs, and the 

 main part of the vascular system. Thus it becomes necessary to 

 make distinctions between the body-cavities of Adinotrocha and 

 those of the adult and to call them respectively by different names. 

 The former may be termed the larval ]>ody-cavities, and the latter, 

 the adult body-cavities. 



Most pi'cvious writers have not taken any particular notice of 

 the relation which exists between the external body- division s and 

 the body-cavities of Actinotroeha, so the words " hood " and " foot " 

 do not denote anvthino- but mere external features. The idea of 

 segment was first introduced by Caldwell ; he considers the larval 

 body as diN-ided into three parts : (1) the preoral lobe set in front 

 of the septum, (2) the ti-unk portion situated behind the septum, 

 and (3) the foot or invaginated pouch. According to this view, 

 the body-cavity is divided by the septum into two contiguous parts, 

 vh., the preoral cavity in front of, and the trunk cavity behind, 

 the septum. Masterman divides the entii'c liody into three 

 portions, viz., the preoral lobe, the collar, and the trunk. These 

 three divisions are not only externally marked by their respective 

 forms, but also l)y the presence of two transverse septa or mesen- 

 teries. Thus we see, the preoral lobe of Caldwell comprises l»oth 

 the preoral lobe and the collar of ^NTastermax. 



Whatever may be the value of j\[asterman's Diplochorda 

 hvpothesis, T fool inclined to acco])t with some modifications, his 



