88 RECORD OF CURRENT RESEARCHES RELATING TO 



investigated in 1826 by K. E. von Baer, who described two delicate 

 bright bands following a longitudinal course and placed in the 

 ventral region of the body, Duges, two years later, described a 

 system which he looked upon as being vascular ; it consisted of two 

 primary longitudinal trunks passing into one another at either end, 

 and connected by transverse anastomoses ; this is the nervous system 

 as described by Dr. Lang. It was not till 1848 that any further 

 details as to a nervous system were given by any anatomist ; but 

 in that year Quatrefages described a " double ganglion " Avhence 

 radiated nerves, and which was situated in a " lacuna " of the body. 

 The circulatory system of Duges was regarded as being of a nervous 

 natiu'e. Various later anatomists have also contributed to the litera- 

 ture of the subject, and among these the most notable are Metschnikoif 

 and Moseley. 



The author's own investigations have been singularly aided by 

 a most fortunate discovery in the shape of a marine Planarian of 

 complete transparency, a pair of which were found in March 1878, 

 in the neighbourhood of Punta di Campauella; for the present 

 he places this new form in the genus Planocera, and gives it the 

 specific name of Graffii. Without compressing the animal in any way 

 he was enabled to investigate its structure under a magnifying power 

 of 300 diameters ; the enteric canal was very distinct, and finely 

 branched ; what was most striking was the presence of a delicate 

 network of colourless cords, with a sharp contour, most easily visible 

 in the outer regions of the body ; the meshes of the network, which 

 increased in size from within outwards, were distinctly polygonal in 

 form. Towards the middle of the body the cords increased in thick- 

 ness, and passed into a number of well-developed trunks, which all 

 converged to a common centre ; this centre is a transparent bilobed 

 knot, which is placed between and behind the two conical tentacles 

 which are found at the end of the anterior thii'd of the body, and in 

 front of the proboscis ; in position and in form this knot had just the 

 same characters as the " brain " of Proceros, Leptoplana, and other 

 marine Planarians. The brain, therefore, is a largish knot, transversely 

 oval in form, and not very distinctly divided into two lobes ; entirely 

 homogeneous when looked at under a low power, it is, imder higher 

 magnification, seen to consist of fibrous bands, and of ganglion-cells. 

 A large number of nerves are given off from it, and these are so large 

 and so numerous that it is difficult to make out the proximal portion 

 of their course ; ten or eleven nerves could be counted on either side 

 of the middle line, while in the middle itself there ran an unpaired 

 and thinner nerve ; the strongest are those which pass most far back. 

 A short distance from the brain the ten largest nerves are connected 

 by a commissure ; and as we trace them through the body we find 

 that they and their branches are constantly connected together by 

 fine anastomosing nerve-filaments; and this whole system may be 

 seen to lie under the digestive system and the generative organs ; it 

 is only the optic and tentacular nerves which take on a dorsal position. 

 The brain lies in a pyriform space (lacuna of earlier observers), 

 which is formed by the separation from it of the pigment of the 



