PHORONIS ARCHITECTA— BROOKS AND COWLES. 89 



However, larvae which we have examined, fixed in Flemming's fluid, have not shown the vacuoles 

 to be tilled with fat droplets as Longebamps states. 



Sections tli rough the diverticula of quite old larvae (fig. 35) stained with iron hsematoxylin 

 show columnar cells, nearly every one of which contains a deeply staining body about one-quarter 

 the size of the nucleus. The bodies are not found in the wall of the stomach proper, and we 

 believe that they give the yellowish-brown color to the diverticula of the live Actinotrocha. 



In some cases we have found old larvse in which the cells of the diverticula were vacuolated, 

 but in these cases we have also found that the entire stomach wall was vacuolated. The vacuoles 

 were never large enough or numerous enough to alter the natural position of the nuclei. 



According to Masterman's description, the first vacuoles are formed at the distal ends of the 

 cells and more vacuoles arise later between these and the inner ends of the cells. As far as we 

 know, the origin of vacuolated tissue in vertebrates is the reverse of this, the vacuolization 

 beginning at the center of the cord and traveling outward. 



The specimens of Actinotroch.se of Phoronis sabatieri which we have examined show the struc- 

 ture of the stomach diverticulum to be very similar to that of the diverticulum in the Actino- 

 trocha Species B. The diverticulum, however, is somewhat more vacuolated in the former than 

 in the latter, but it does not show the peculiar structure which Masterman has described for the 

 "notochord" of the species from St. Andrews Bay. 



It is hard to see what use the Actinotrocha has for any organ of support in the region where 

 the diverticula are found and it seems much more probable that they have a glandular function. 



Nervous system. — It is generally admitted among investigators who have studied the 

 anatomy of the Actinotrocha carefully, that the creature has a subepidermal layer of nervous 

 tissue throughout the body which is fibrillar in character. This nervous tissue assumes the form 

 of quite definite tracts in certain parts of the body in Actinotrocha Species Ii. and fairly well- 

 developed nerves can be said to twist. The most conspicuous ones are found in the median 

 dorsal line of the preoral hood as three distinct longitudinal bundles of nerve fibres extending 

 from the ganglion to the anterior edge of the hood. There are other tracts which, though they 

 are not as definitely marked out as the above, are undoubtedly nerves. 



Masterman (15) in his work on the anatomy of the Actinotrocha from St. Andrews Bay has 

 described a complicated nervous system, but the investigations of Roule (20), Ikeda (It), and Long- 

 champs (12) have thrown considerable doubt on the correctness of his observations. Whether 

 these differences have been due to differences in the Actinotroch.se. studied by these workers or 

 whether they are due to the technique it is impossible to say. but. judging from the difference 

 in the degree of development between the nervous system in Species A. and Species B., we all- 

 ied to believe that the disagreements are due partly to the fact that no two of these investigators 

 have studied the. same specie- of Actinotrocha. 



While the nervous system of Species A. can with careful study be shown to be very similar 

 to that of Species B., yet it is so feebly developed that without first having studied Actinotrocha 

 Species B. we should not have been able to see the similarity in the disposition of the different 

 nervous tracts. The ganglion with its three dorsal longitudinal nerves running along the median 

 line of the hood is easily seen in the live larva of Species A., but in sections we have found it 

 impossible to trace the latter. The sensory papilla mentioned in the description of the Actino- 

 trocha Species B. is absent in this species. 



We are pleased to be able to confirm, to some extent, Masterman's (15) description of the 

 nervous system of the Actinotrocha, especially since a shadow of doubt has been cast upon his 

 work by some who have studied the Actinotrocha. 



Partly because Species B. seems to be a much more highly developed ActinoProcha than 

 Species A., and partly because of its similarity to the one that .Masterman studied (which is of so 

 much theoretical interest), we shall confine the description and figures to the nervous system of 

 Species B., although we are convinced that this Actinotrocha is not that of Phoronis architected 

 but of an adult that has not been discovered. 



