286 A. T. MASTERMAN. 



PART I. 



The Structure of Actinotrocha. 



Literature. 



As is well known, the larva, Actinotrocha, was first de- 

 scribed by J. Miiller (16) as occurring in the North Sea. He 

 gave an account of the general characters, the form of body, 

 number of tentacles, &c. This was followed a year later by a 

 research of Wagener, who, assuming the animal to be an adult, 

 gave a description of its anatomical features. His work was 

 conducted, as far as can be ascertained, without the assistance 

 of sections, and it will be referred to in the following pages. 

 It is evident that some of his statements are erroneous, more 

 especially in the section referring to the nervous system. 



In 1850, Siebold (19) contended for the larval nature of 

 Actinotrocha, drawing a comparison with Bipinnaria. 



In 1854, C. Gegenbaur (9) notified the occurrence of a 

 similar form from Messina, in winter, of a small size ("35 mm.), 

 and remarks on the diflFerences from Miiller's. He traced its 

 growth and diflPerentiation to -4 mm., with an accompanying 

 marked elongation of the hind region. 



In 1858, Krohn (11), examining the same species as Gegen- 

 baur, came to the conclusion that it had specific distinctions 

 from that of J. Miiller, mainly in the perianal ciliated band 

 and the pigmentation. He also discovered the fact that its 

 metamorphosis resulted in a gephyreau worm. 



In 1862, A. Schneider (18) described and figured a new 

 species, A. pallida, and gave an account of the metamor- 

 phosis into the worm-like " Sipunculid '' afterwards identified 

 as Phoronis. His description of the larval anatomy con- 

 firmed in most particulars that of his predecessors, but he cor- 

 rected Wagener on some points, such as the blood-system. 

 His description and that of Claparede (5) of the " notochord " 

 are of special interest. His observations on the adult worm 

 led him to find its nearest allies in Phascolosoma, Sipun- 

 culus, and Aspidosiphon. 



