24 HISTORY OF THE SUBJECT. 



while the Nemerteans are Turbettaria dioiques. As regards the separation of the sexes, the 

 Nemerteans approacli the Nematoda, but the configuration of their organs is entirely dissimilar. 

 He hints at other differences in connection with the teguments and form of the body, but adds that 

 in a rigorous examination these are of secondary importance. He concludes with the following 

 remarks : — "Thus having shown how the Nemerteans differ from the Planarians in their entire 

 organization, having exhibited these differences to be profound and characteristic, havino- 

 demonstrated how far they diverge from the Nematoda in essential structure, we arrive at the 

 necessary conclusion that the Nemerteans constitute a group quite unlike those with which 

 Ave have been contrasting them, and that their affinities do not link them more closely to the 

 Nematoda and Anevormes in general than to the Planarians in particular." The author thus 

 rather exaggerated the gulf between the latter and the Nemerteans, being misled by the 

 erroneous observations of M. de Quatrefages on the digestive system. 



In the same paper M. Blanchard goes on to describe Cerebratidus lij/uricus, one of the 

 Anopla, chiefly with respect to its circulation. He mentions that on account of the delicacy of 

 Nemertean tissues he had to add a small proportion of a salt of mercury to the sea- water, so as 

 to enable him to inject the vessels. He states that the dorsal vessel shows no ramifications, but 

 passes forwards to the cephalic region to unite with the two lateral vessels by the communications 

 around the proboscis and nerve-centres, the latter being bathed by the circulating fluid. He 

 contrasts this arrangement with the observations of M. de Quatrefages, but he was not aware 

 that essential differences exist in this respect between the Anopla and Enopla. He saw trans- 

 verse ramifications between the lateral vessels, and appears to have noticed the network in the 

 oesophageal region, though he speaks of an internal lateral vessel, of whose presence we are 

 unacquainted. He thought that transverse ramifications of the longitudinal vessels existed in all 

 the Nemerteans, for he also observed them in Folia geniculata, Delle Chiaje, and in a Valencinia 

 of undetermined species ; and agreed with M. de Quatrefages as to the presence of proper walls to 

 the vessels. The Nemerteans, therefore, have a vascular network comparable with that in the 

 Anevormes, presenting nevertheless differences in anatomical disposition. The circulatory 

 apparatus in these worms is perhaps more complete than that of the Aporocephales (Planarians) 

 or the Trematoda ; for the dorsal vessel seems to carry the blood forwards, and the lateral 

 backwards, though the oscillations are irregular. He would place the Nemerteans, consequently, 

 in a division adjoining the Anevormes, both on this account and the higher development of their 

 nervous system. 



Yon Siebold, 1 in 1848, took the bold step of severing the Nemerteans from the Planarians 

 by the intervention of the Rotatoria ; and though we would not approve of such disjunction, the 

 soundness of his decision in separating them from the Helminths can scarcely be questioned. He 

 arranged them as the first Order of the Ringed worms : — 



Order I. Apodes. — Body without bristles. Sub-order 1. Nemertini. — Body posteriorly 

 without an anus (Ausangeorgane) ; head often with lateral respiratory fissures. 



His information is derived from Rathke and other observers. 



This author subsequently gave abstracts of various papers on the Nemerteans in the c Archiv 

 fur Naturgeschichte.' 2 



1 c Lehrbuch der Yergleichenden Anatomie/ von Y. Siebold u. Stannius. Berlin, 1848. 



2 ' Archiv fur Naturgeschichte/ 1850, p. 382, &c. 



