V 



652 GEEARDA STIASNY-WIJNHOFF 



built like that of all Anopla and of all Monostilifera, and that 

 this wall in the Polystilifera is found in the pelagic genera Nato- 

 and Nectonemertes and the family Balaenanemertidae as well. 

 , ^ That the interlacing of these two original muscle-coats, which 



\ is characteristic of all Polystilifera Reptantia and elsewhere 



is unknown, is also found in many Pelagica ; that the process 

 of interlacing seems to start in the hinder part of the rhyncho- 

 coelomic cavity and proceeds proximally, as shown in Pelago- 

 nemertes. That we see the penetration of the two layers go 

 on in Dinonemertes and Armaueria, and that the interlacing 

 is completed in all other genera of Pelagica and in the Reptantia. 

 That in one genus this process resulted in the inversion of the 

 original layers, i.e. the aberrant genus Biirgeriella, where the 

 proximal part of the sheath has the basket-like structure 

 characteristic of Polystilifera, and the distal part, as in Pelago- 

 nemertes, shows the result of this process. 



If we look at the digestive tract three remarkable 

 points are to be distinguished. The position of the mouth 

 under the brain w^as stated to be very primitive in armed Nemer- 

 teans and even in Polystilifera to be quite unusual. As to the 

 oesophagus we have the statement of Brinkmann that this 

 part of the stomodaeum is absent in all Pelagica with the only 

 exception perhaps of Planktonemertes. His fig. 23, PI. xiii (4), 

 gives no right to compare this small oesophagus with that of 

 Siboganemertes (Text-lig. 11) ; after his description on p. 24, 

 however, we can hardly speak of an oesophagus, and truly can 

 say in Pelagica the oesophagus is absent, as in the unarmed 

 genera. But in the Reptantia a w^ell-developed oesophagus is 

 always, in the Monostilifera, as a rule present. We know its 

 absence in Amphiporus marmoratus (Biirger) (6, 

 PI. xvi, fig. 1), though in Amphiporus marmoratus 

 (Joubin) it is well developed as in most other species (12, 

 p. 564, fig. 4). This figure interests us still more because the 

 different parts of the stomodaeum with the exception of the 

 oesophagus show about the same features as Siboganemertes. 

 The pyloric tube of Joubin 's species is much wider than in 

 our specimen, but it opens into the gastric cavity at the same 



