96 MR. K. c. PUNNETT ON [May 21, 



following table, whicli refers to the ventral surface in the middle 

 of the body : — j^ 



Epithelium 110 fi 



Basement-membrane 75 yu 



Circular muscle 2>5 jx 



Longitudinal muscle ] 85 // 



The epithelium is relatively somewhat higher dorsally. The 

 basement-membrane is considerably thinner below the epithelium 

 of the head-furrow. Powerful dorso-ventral muscles occur 

 throughout the body behind the brain. 



The vascular system shows the ordinary arrangement, such as 

 has been figured by Oudemans^ for B. sjjectabilis {=ruhrostriatus). 

 The alimentary canal offers no points of special interest. There 

 is a short well-marked proctodseum lined by comparatively low 

 epithelium. The first pair of blind-gut pouches reach forwards 

 and lie against the hinder portion of the cerebral organ. 



The proboscis- sheath exhibits the peculiar basket-work arrange- 

 ment of the circular and longitudinal muscle-fibres characteristic 

 of the genus. It possesses also the peculiar diverticula. In this 

 species they are slender with a fine layer of muscle-fibres, and the 

 whole surrounded by a layer of parenchyma-cells (Plate VI. fig. 

 4, rcl). The 1st two diverticula unite with one another anteriorly 

 (cf. D. lankesteri Hubrecht, Challenger Eeports, vol. ix. p. 106). 

 They form an irregular network which extends anteriorly over the 

 brain and here gives off a number of large expansions (Plate VI. 

 fig. 4, rde) whose wall consists only of the rhynchocoelomic epi- 

 thelium — the muscular and parenchymatous layers disappearing. 

 Consequently in the cerebral region we meet with 4 distinct sets 

 of cavities lying in the gelatinous connective tissue, viz. : 



(1) Blood-vessels. 



(2) Excretory tubules. 



(3) Ehynchocoelomic diverticula and their expansions. 



(4) Irregular spaces in the connective tissue (Plate VI. 



fig. 4, cts.). 



The proboscis is well developed and of about the same length 

 as the body. Its epithelium is raised up into large papillae, and 

 through the extremely thick basement-membrane, upon which they 

 rest, may be traced strong nerves entering their bases. The pro- 

 boscis contains 14 nerves and is attached near the end of the body 

 to the ventral wall of the proboscis-sheath. 



The excretory system reaches forward to the cerebral organ, 

 and backward some way along the posterior division of the 

 oesophagus (" Magendarm ")■ The duct is situated at the level of 

 the hind end of the cerebral organ. The tubules lie closely round 

 the lateral nerve-cords. 



The gonads are large and arranged in three rows either side, which 

 all open on the dorsal surface. They take the form of elongated 

 ^ Loc. cit. pi. i. fig. 7. 



