Miscellaneous. 427 



lengths ; some of them reach the ventral shield. These muscles cause 

 the invagination of the anterior part of the trunk, the protraction 

 of which is brought about by the posterior transverse muscles, which, 

 by contracting, drive forward the fluid of the general cavity. 



The digestive canal at first travels from before backwards, bends 

 round near the perforated plates, returns forward, then turns again 

 backward to terminate at the anus : it forms numerous convolu- 

 tions, and is further irregularly twisted spirally with the generative 

 organs. We may distinguish in it the following regions: — 1, a 

 wide, short, protractile pharj^nx, in the form of a bulb, presenting 

 glandular ridges ; 2, a much narrower and longer oesophagus, which 

 is analogous in structure to the stomach, but is destitute of the vibra- 

 tile furrow, and its less developed epithelial layers possess no 

 granulations ; 3, a stomach considerably wider than the other parts 

 of the intestine, and composed of the peritoneum, of a feeble 

 muscular layer, the scattered fibres of which are partly longitudinal, 

 partly transverse, and of a greatly developed glandular epithelium 

 which forms prominent longitudinal ridges in the interior ; at the 

 commencement of the stomach originates a vibratile furrow, which 

 only stops at the terminal part of the intestine ; the stomach secretes 

 a 3-ellowish liquid which gives a green colour with Gmelin's and a 

 red colour with Pettenkofer's reagent ; I think it may be regarded 

 as bile ; 4, a recurrent intestine, and, 5, a posterior intestine, which 

 I distinguish from each other principally because of their general 

 direction, and to facilitate a more detailed description ; their struc- 

 ture essentially resembles that of the stomach, except the smaller 

 development of the epithelium, which is here no longer glandular ; 

 6, a protractile terminal intestine, destitute of the furrow and pre- 

 senting the structure of the external skin. 



The nervous system consists of two cerebroid ganglia, of a wide 

 collar embracing the pharynx, and of a ventral cord, which widens 

 considerably behind over the shield, in consequence of a greater 

 development of its connective elements. On its ventral surface this 

 cord gives off numerous unpaired nerves, directed downwards and 

 backwards, which afterwards bifurcate into two symmetrical 

 branches. I have not yet completely elucidated the question of the 

 relation of these branches with the granular layer and the nervous 

 filaments mentioned above. 



The branchial filaments, destitute of cilia, have their internal 

 cavity divided longitudinally by a fibro-muscular partition ; the 

 two elongated sinuses thus formed communicate by a loop at the 

 free extremity of the filament, and unite to form a single canal near 

 the point of insertion upon the perforated plate. In the living 

 animal we see some of these filaments elongated in the water, which 

 they beat ; the red blood contained in them enables the loop formed 

 by the two sinuses to be recognized ; but most of the filaments 

 are usually retracted and spirally rolled up by the contraction, 

 of the longitudinal muscles which line the two sinuses, and 

 which drive back the blood to the interior of the body, whilst the 

 elongation of the branchioe makes it flow into them. At the point 



