1876.] 25 [Minot. 



of all those classes of animals indicated in the title, and then 

 attempts to connect the Plathelminths through the Nemertines with 

 the Annelids. It seems to me that he fails of success, for he bases 

 his conclusions mainly (1) upon the idea that the two lateral nervous 

 cords are really present in the Planarians, and (2) upon some obser- 

 vations which he himself made upon Microstomum. As regards the 

 first point, I have already stated that Mosely and myself, the only 

 investigators who have extensively applied modern methods of micro- 

 scopical research to the study of the Pharyngoccela, were unable 

 to find these supposed nerves, though we discovered other cords 

 formed of parenchymatous tissue, which run where the supposed 

 nerves were said to be, and I know of not the slightest reason for 

 not thinking that the observation of these cords led earlier writers to 

 describe the imaginary lateral nerves. The mistake was the more 

 natural since the parenchymatous cords run close up to the central 

 nervous ganglion. As regards the second point, it is undoubted that 

 Prof. Semper' s observations reveal similarities between Microstomum 

 and the Nemertines, but in so doing I think he cuts off all possibility 

 of connecting it any longer with the Platthelminths. He says that 

 it has an oesophageal nervous ring, 1 which, combined with its peculiar 

 reproduction by division, 2 is sufficient to indicate that it is not a 

 Plathelminth. The structure of the sexual organs, when it shall be 

 known, will decide the question. Search should be made for a yolk 

 gland, and for special genital ducts, such as characterize the flat 

 worms, and for genital sacks arranged in pairs and without a common 

 efferent duct as in the Nemertines. At present certainly Microsto- 

 mum cannot be considered to link the Plathelminths with the Ne- 

 mertines, nor to remove the former class from the singularly isolated 

 position in which we are obliged to place them, for the time being at 

 least. I have here entered into this subject because it appears desira- 

 ble to show that the belief, that the Planarians belong in the system 

 of classification near the point where the various forms of bilateral 

 animals branched off, is without sufficient basis. In other words, it is 

 not yet known to what animals lower in the scale the Nemertines 

 and Annelids are related. 



Mr. Minot also exhibited and described the " sledge micro- 

 tome," made by Leyser of Leipzig. 



* L. c, p. 369 ff. 



a Cf. Graaf. Zeit. f. wiss. Zool., xxv (1874-75), p. 408. 



