92 Proceedings of the Royal Society of Victoria. 



dorsal surface of the body, doubtless in relation to the crawling 

 movements of the animal. In transverse sections it is very 

 clearly seen to be broken up into blocks by small bundles of 

 muscle fibres which lun inwards from the circular sheath to 

 the deeper parts of the body (Figs. 8, 24). 



The layer of diagonal or oblivpie muscle fil)res (Fig. 10,o. m.) 

 is very thin and consists of two series of fibres crossing one 

 another obliquely, just as in Geoplana,^ oi^ly in a different 

 position. This diagonal layer in Geonemertes australiensis 

 is very clearly recognisable in tangential sections along the 

 sides of the body, much as is represented in Figure 10, taken 

 from a specimen stained with borax carmine. I should not 

 like to say positively that it extends completely round the 

 body, but it probably does, though 1 have not been able to 

 detect it with certainty in the mid-dorsal and mid- ventral 

 regions. 



In the head-region tliere is a special and very important 

 development of muscles in relation to the proboscis sheath 

 {vich Figs. 2, 3, 4, 5, 6). At about the level of the centre 

 of the cerebral ganglia the longitudinal muscle sheath splits 

 into two layers, an inner and an outer. The outer layei- 

 (I.' ni.') passes forwards in the old position. The inner layer 

 (m. d), on the other hand, passes forwards and inwards to 

 join the proboscis sheath at the place where the proboscis 

 is attached to it, immediately in front of the cerebral ganglia 

 and behind the mouth. There is thus formed a distinct 

 muscular diaphragm (Figs. 2-6, m. (/.), convex anteriorly, 

 lying immediately in front of the cerebral ganglia and 

 behind the mouth. The musculature of the proboscis and 

 its sheath, with which this muscular diaphragm is continuous, 

 will be desciibed in dealing with those organs. 



I have already mentioned that numerous small bundles of 

 muscle fibres run inwards from the region of the circular 

 muscle sheath through the longitudinal sheath to the dee[)er 

 parts of the body. Many of these small bands unite together 

 to form a series of strong dorso ventral muscular bands 

 which run in a, vertical direction between the lateral 

 diverticula of the alimentaiy canal. 



c. Alimentary Caiud. 

 The alimentary canal agrees very closely indeed with that 

 of Geonemertes chalicophora, as described and figured by 



* Vide Dendy " Anatomy af an Australian Land Plauarian," Trans. Eoyal 

 Soc. Victoria, 1889. 



