20 HISTORY OF THE SUBJECT. 



a paper on Planaria and Nemertes, promulgating those views, which afterwards were given at 

 length in his ' Entwurf/ and w r hich therefore need not be further alluded to here. The Nemer- 

 teans especially are curtly dealt with. 



H. Rathke, in a very excellent structural chapter in 1843, 1 amended the errors of Dr. Johnston 

 in regard to the mouth in Lineus, and described correctly the digestive system, the position and 

 relations of the proboscis and other points. He was inclined to think the proboscis an organ of 

 touch. 



In the same year (1843) we have the forerunner of a series of elaborate investigations by 

 M. de Quatrefages, 2 who notified to the Academy that he had found separate sexes in the 

 Nemerteans, with the development respectively of ova and spermatozoa, as in the Annelids. He 

 promised to make known the complete results at a future period. 



M. Milne Edwards, 3 in reporting on the papers of M. de Quatrefages, in 1844, states, with 

 regard to the Nemerteans, that the latter found that they approached the Annelids in the general 

 distribution of their vascular system, the leeches in the structure of their buccal apparatus, and 

 other points in their organisation ; yet their reproductive organs were analogous to those of many 

 helminths. Their nervous system he compared to that of the " Lingules," and he likened their 

 digestive system (with a csecal termination) to that of the lower helminths and zoophytes. The 

 majority of these homologies are placed on no reliable data. 



In 1844 A. S. CBrsted contributed a valuable addition to our knowledge of the Nemerteans 

 and allied genera. 4 He classed the Nemerteans as the fourth sub-order {Cestoidina) of his order 

 Apoda, the others in their respective positions being (3) Trematodina (Hirudinea and Planariea), 

 (2) Acanthocephalina (Siphunculacea), and (1) Nematoidina (Gordiea). The sub-order Cestoidina 

 was thus characterised : — " Body linear, rounded rather than flattened, much longer than broad, 

 indistinctly marked by soft annulations, covered with vibratile cilia; distinct muscles, but no true 

 nerves (?). Eyes 2, 4, 6, 8, 10, many or none. Respiratory organs absent or in the form of 

 lateral fissures on the head, which conduct the water to the proximity of the hearts. Complete 

 circulation with two hearts. Digestive tube simple, with the aperture of the mouth situated 

 ventraliy (rarely terminal), and a terminal anus. Sexes separate ; in each a stimulating 

 copulating organ. Testicles and ovaries similar in structure except as regards contents (ova or 

 spermatozoa), numerous, and placed laterally in each segment." The author thus confounded the 

 ganglia with hearts, and hence was led to believe that the cephalic fissures were connected with 

 respiration, in so far as they permitted a closer relation between the sea- water and the contents 

 of the supposed hearts. He had a fair notion of the digestive system, but he misinterpreted the 

 physiology of the proboscis, He arranged the sub-order into two families and eight genera, 

 thus : — 



1 ' Beitrage zur Fauna Norwegens,' &c, pp. 231—237. 



2 ( Comptes Rendus/ torn, xvii, Dec, 1843, p. 424. 

 s ( Ann. des sc. nat./ 3eme ser., torn, i, pp. 20-21. 



4 ' Entwurf einer systematischen und speciellen Beschreibung der Plattwurmer/ &c. Copenhagen, 

 1844. 



