88 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



in the position in which Masterman finds the atrial grooves." In those cases in which the hood 

 remains in its normal position we have seldom found Masterman's so-called 'atrial grooves," and 

 even in a few cases when' the hood is turned upward they have been absent. 



The ventral wall of the hood just as it passes into the wall of the oesophagus not infrequently 

 shows a pair of bilaterally situated grooves which are similar to those found on the ventral collar 

 wall. 



X> uroport " (Masterman). See section on the nervous system. 



"Sub-neural sinus" (Masterman). Another organ which Masterman (15) has described is a 

 sinus immediately below the nerve ganglion, caused by the want of contiguity between the 

 raesoblastic walls of the preoral cavity and the collar cavity. This sinus, he claims, is closed 

 except for a fissure which leads eventually into the dorsal blood vessel. He compares this sinus 

 to the heart of Balanoglossus. 



Menon (19), as far as we know, is the only other worker on the Actinotrocha who claims that 

 there is a definite vesicle beneath the ganglion and he has discovered no connection between its 

 cavity and the dorsal blood vessel. 



Roule, Longchamps, and Ikeda do not find this organ, but the latter recognizes the existence 

 of a space ("posterior recess") free from mesenchymatous fibres, which is the posterior part of 

 the preoral lobe. This, however, he says, does not connect with the dorsal blood vessel. 



From the study of the early development of Phoronis architecta and the origin of the 

 mesentery between the hood and the collar, we have come to the conclusion that no vesicle is 

 formed in that species between the two layers of the mesentery (if two layers exist). The 

 mesentery which forms the posterior wall of the preoral lobe cavity is found attached just back 

 of the ganglion in the median line and there is not the least sign of a vesicle other than the 

 cavity of the preoral lobe (tig. -M). 



In neither Actinotroclm Species A. nor Actinotrocha Species B. have we found a vesicle below 

 the ganglion, although in both cases there is a space such as Ikeda (9) has seen, free from mesen- 

 chymatous fibres. The anterior boundary of this space is rather sharply defined and occasionally 

 among longitudinal sections a fibre with a nucleus is seen running vertically from the dorsal to 

 the ventral wall of the hood, giving the appearance of an anterior wall to the space. These 

 tibres, however, are very much more delicate than the wall of the collar lobe septum, and what is 

 more, they occur only occasionally and are evidently not sections through a membrane. 



In the Actinotrochse,, which we have examined, there does not exist any vesicle beneath the 

 nerve ganglion nor any structure which could be likened to the heart vesicle of Balanoglossus. For 

 the supposed relation of the dorsal blood vessel to the "subueural sinus," see Blood system. 

 "Stomach Diverticula 1 '' (Ikeda, Longchamps, and Menon). 

 " JVbtochords" (Masterman and Roule). 



Ever since Johannes Midler (19) saw the paired "blinddarme" in Actinotrocha branchiata 

 nearly all of those who have studied Actinotrochse have observed the same structures. Some 

 have considered them to be liver diverticula, others have described them as dark masses with 

 globules and as brown specks. Wilson calls them "glandular lobes of the stomach." 



Ikeda (9), Longchamps (12), and Menon (17) speak of them as "stomach diverticula," but 

 they do not ascribe any function to them. Masterman (15) and Roule (20) look upon them as 

 rudimentary notochords. Roule, Ikeda, and Longchamps have studied larvae in which the 

 diverticulum was not paired and lateral, but unpaired and medio-ventral. The latter investigator 

 has observed larvae of both t\ \<. 



We find that in Species A. the diverticulum is undeveloped even at the time of metamorphosis 

 while in Species B. the diverticulum is paired, well developed, and ventro-lateral. 



Longchamps has very justly objected to Masterman's use of the name " Diplochorda" nndei 

 which the latter includes the Phoronidse and Cephalodiscus. 



The diverticula of Species B. do not show the regularly arranged vacuoles which Masterman 

 has described for the Actinotrocha from St. Andrews Bay. In fact, we agree with Longchamps's 

 (12) observations in finding the histological characters absolutely different in Species A. and B. 

 from the histology of notochords, and there is not the least indication of supporting tissue. 



