648 GERARDA STIASNY-WIJNHOFF 



place as the nerves of all Enopla, on the inner side of the inner 

 longitudinal musculature. Ho we have to look for the inner 

 circular muscles of these genera behind the brain, and not 

 before it. If we ask where the brain lies exactly in Pendo- 

 nemertes and Balaenanemertes, PI. v, fig. 1. PI. xiv, fig. 19, 

 PI. XV, figs. 3 and 4, PI. xvi, figs. 17 and 18, of the monograph 

 (4) show us that it really is found betw^een two layers of longi- 

 tudinal musculature. Whether the outer layer consists of 

 strands that go to the body-wall (' Eiisselfixatoren ') or of the 

 inner parts of them that still have to join the wall of the cavity, 

 is not clear. But in any case it i s certain that we can expect 

 the inner circular muscle-layer only behind the brain and not 

 before it. Wherever Brinkmann describes the exact rela- 

 tions of the muscle-layers in these parts, it invariably is men- 

 tioned that the first traces of the outer circular musculature 

 of the proboscis sheath are found behind the brain. This cannot 

 always be so, for I know cases in the Eeptantia where the remains 

 of the circular musculature of the body-wall are found around 

 the hinder parts of the brain, and in this case it is evident that 

 the contact with the rhynchocoelomic part of this layer must 

 be looked for before the brain. In such cases we must expect 

 the outer circular musculature of the sheath to be in the 

 nerve-ring. In others I noted the same beginning of this layer 

 as Brinkmann, i. e. behind the nerve-ring. 



The wall of the cavitj^ before the brain is built differently 

 in different cases. It is interesting to note that in one IMalayan 

 species all circular muscle-fibres are absent in front of the brain, 

 in another all longitudinal, and always the interlacing begins 

 behind the nerve-ring. B r i n k m a n n describes in all his genera 

 of Pelagica the presence of an inner circular muscle-layer 

 (as the direct continuation of the new proboscidian layer) 

 before the brain and outside of it a longitudinal layer w^hich, 

 he says, passes through the circular musculature behind the 

 brain and so comes to lie inside (Text-fig. 19). If, however, 

 this really was a passing through we should find an interlacing 

 of fibres at this place. Though Brinkmann is very exact 

 in his statements he never mentions this, and his figures show 



