NEPHRIPTA OF THE ACTINOTROCRA LARVA. 105 



also the ruflimonts of a dorsal vessel and a vascular space 

 round the stomach, which arise as " splits in the splanchno- 

 pleure." "The septum," says Caldwell, "is attached in a circle 

 along the line of the nerve-ring [at the base of the tentacles], 

 and free communication exists between the body-cavity in 

 front of the septum and the split in the splanchnopleure, 

 which will form the blood sinus and vessels of the adult." 

 He found a ventral mesenter}^ extending from the septum to 

 the anus. " The blood-corpuscles .... arise from the 

 raesoblast cells in front of the septum." As we shall see, this 

 description is in the main correct, and Caldwell failed only in 

 that he did not observe a separate coelomic cavity in front of 

 the septum. 



Since Caldwell, Masterman published, in 1898, a paper on 

 Actinotrocha (11), in which many alleged new features are 

 described; K. Ramunni Meuon has contributed some notes 

 on an Indian species (13) ; de Selys Longchamps has dis- 

 cussed the development and structure of certain European 

 forms (16) ; whilst Iwaji Ikeda has brought forth a most 

 valuable paper on the larval history of P. ijimai from Japan 



(9)- 



Masterman appears to have been so strongly influenced by 

 theoretical prejudices in his interpretations of the structure 

 of the larva that his account cannot be accepted as trust- 

 worthy. Of the several important new points described by 

 this author the following may be mentioned : — The presence 

 of two "proboscis pores:" "on either side of the middle 

 line, near the nerve-ganglion, a pore leads by a short canal 

 into the coelomic cavity of the pre-oral lobe." The " neuro- 

 pore : " "a long sac-like diverticulum lying under the nerve- 

 ganglion." The notochord-like character of the gastric 

 caecum. The " subneural gland:" a diverticulum of the 

 oesophagus projecting inwards below the brain. The "sub- 

 neural sinus:" "there is just under the nerve-ganglion a 

 large sinus caused by a want of continuity between the 

 mesoblastic walls of the pre-oral cavity in front and the 

 collar cavities behind. ... At the posterior end of the 



