NEPHEIDIA OF THE AGTINOTROCBA LARVA. 109 



front of the main septum. Basing his nomenclature on a 

 comparison with Balanoglossus and Cephalodiscus, Masterman 

 (11) speaks of two distinct coelomic cavities — an anterior 

 pre-oral coelom in the hood and a larger coelomic cavity, 

 which he calls the "collar" cavity, separated from the first 

 by a complete septum below the brain, and reaching back to 

 the main and more posterior septum. Whilst, according to 

 this author, the "collar" coelom couimunicates with the 

 exterior by means of the two nephridia, the pre-oral coelom is 

 said to open to tlie exterior by two " proboscis pores," one 

 on each side of the ganglion. Moreover a separate '' sub- 

 neural sinus" is supposed to exist, lying between the two 

 layers of the anterior septum, and to communicate with the 

 longitudinal dorsal blood-vessel. 



Now Caldwell (2) describes only the single main septum 

 separating a truuk coelom from a pre-septal blood-cavity in 

 front, occupying both the hood and the region behind it, 

 aud continued backwards iuto the longitudinal blood-vessel. 

 This single extensive cavity may be called the " pre-septal 

 cavity," to avoid all morphological prejudice. Menon (13), 

 de Selys Longchamps (16), and Ikeda (9), all three deny the 

 existence of " proboscis pores." I have no hesitation in 

 saying that no such pores exist in any lavvas I have examined, 

 whether from Faro or from Trincomalee. 



Menon, on the other hand, appears to confirm Masterman's 

 statement as to the existence of a complete septum separating 

 a "pre-oral" from a "collar" cavity; but his account is 

 inadequately illustrated, and by no means convincing. 

 Whilst the alleged septum is said to be attached just 

 behind the nerve-ganglion, it is drawn (PL 26, fig. 6) in a 

 position well behind the hood itself. The " pre-oral " cavity 

 is said to contain " scattered blood-corpuscles and ccelomic 

 corpuscles," and to be of a nature " which it is thus difficult 

 to decide." There is reason to believe that Menon has, 

 moreover, confused the true pre-septal ccelom (c. c. in his 

 figures 2, 3, and 4) with the pre-septal heemocele (c. c. in his 

 figures 5, 6, aud 8). According to Menon the " subneural 



