PHORONIS ARCHITECTA— BROOKS AND COWLES. 87 



same special way that they do in Actinotrocha oranchiata (found near Helgoland and described 

 l>v J. Midler (19); and Masterman (15) says in his paper that the form he worked on "does not 

 appear to differ in any essential respect" from Actinotrocha oranchiata. There seems, however, 

 to be considerable difference in size between Actinotrochaoranchiata and Actinotrocha Species B., 

 for, according to Longchamps, the best-developed specimen that he obtained of this species 

 measured 2 nun., while the length of Actinotrocha Species B. averages 1.22 nun. 



Although Actiiiotrnrlin Species A. seems to metamorphose without any difficulty when 

 brought into the laboratory, yet we have never been able to induce Actinotrocha Species B. to 

 do so. Specimens have been kept for ten days or more (the pouch and blood corpuscles being 

 well developed) and in some cases they succeeded in evaginating the ventral pouch, but they 

 were never able to complete the metamorphosis. 



As far as we know, the adult of this Actinotrocha has never been found, but probably it lives 

 under quite different conditions from Phoronis architecta, and it is not improbable that it may be 

 found as a deep-water form. 



INTERNAL ORGANIZATION OF THE FULLY DEVELOPED ACTINOTROCHA. 



•• ShIiiii in-ill ijliiinj" (.Masterman). — Masterman (15) has described a depression in the dorsal 

 wall of the buccal cavity which he terms a "subneural gland" and which he compares with the 

 gland of the same name in the Tunicata and also possibly with the hypophysis of the Vertebrata. 



Roule (2d) anil Ikeda (9) are of the opinion that this depression is a product of the fixino- 

 method. 



Longchamps (12) does not consider it to be an accidental structure, but he does not agree 

 with Masterman's view as to its theoretical significance. 



Menon (17) says that the •'subneural gland" first appears in connection with the collar and 

 that during development it shifts forward into the preoral lobe, but in another part of his paper 

 he says the (esophagus is often folded transversely (this also the case in the young Phoronis) into 

 pouches and the "subneural gland" is a diverticulum of its dorsal wall. 



While in examining sections we have frequently found a depression in the region that Mas- 

 terman (15) indicates, we have never found it in the living larva. Only in very poorly killed 

 larvae have we found the depression to be as deep as Masterman has shown, and in all cases the 

 structure of the wall is practically like that of the oesophagus. 



In the Actinotrochse Species A. and B. there is no depression in the living larva which might 

 be homologized to the subneural gland of higher animals, and we are forced to agree with Roule 

 and Ikeda in their belief that the so-called "subneural gland" which Masterman describes is a 

 product of fixation. 



•• Oral mill atrial grooves" (Masterman). — Masterman (15) has observed a mid-ventral 

 ciliated area leading into the mouth from the preoral lobe in front and a broad ciliated area 

 depressed into two oral grooves leading into it from the ventral surface of the collar area. He 

 has also seen two so-called "atrial grooves" leading into the dorsolateral corners of the mouth. 

 Masterman says he does not find gill-slits in the Actinotrocha, nor does he find structures that 

 he considers to be their homologues. "The atrial grooves" of the Actinotrocha, he says, how- 

 ever, are the analogues of gill-slits (15, p. 319). On page 358 (15), however, he says that 

 "tentatively, I would regard the atrial grooves of the Actinotrocha as the early rudiments of 

 pharyngeal clefts as found in Cephalodiscus." 



His "oral grooves." he says, correspond to the oral grooves in Cephalodiscus. 



Roule (20) does not find the "atrial grooves." but finds two lateral grooves, which he con- 

 siders to be formed by the insertion of the hood on to the collar wall. 



Ikeda (9) and Longchamps (12) are of the opinion that these grooves do not normally exist. 



We have made a careful study of the live Actinotrocha and of surface mounts, but have not 

 been able to make out these grooves in either Species A. or Species 15. Sections, however, show 

 that the "oral grooves" are present, and that in most preparations where the preoral hood has 

 been turned upward by violent contraction (due to the fixing agent) there are two short grooves 



