50 ANATOMY OF THE ENOPLA. 



carcinophila, where the fluid is altogether absent. In Nemertes gracilis and N. Neesii the 

 proboscidian chamber gives way to the blood-vessels posteriorly, the latter, therefore, being the 

 more important structures. The views of Dr. Thomas Williams in regard to the corpuscular 

 liquid, which he termed the " chylaqueous fluid," are so much at variance with accuracy, that I 

 cannot pass them over in silence. He remarks that " in the case of the Borlasiadae, Planariadse, 

 and Liniadae, the chylaqueous fluid is contained in the digestive caeca and diverticula. In some 

 of the Planariadse, however, I have proved that a space does actually exist between the digestive 

 diverticula and the solid structure of the body, which is lined by a vibratile epithelium, and into 

 which probably the external water is in some way admitted. By this water, thus situated, the 

 contents of the digestive caeca are aerated. The fluid oscillating in these caecal appendages of the 

 stomach is thickly charged with corpuscles, which, from their regular character, prove this fluid 

 to have already reached a high standard of organization. They occur as elliptical cells in the 

 Borlasia from which the illustration (fig. 25) was taken ; the fluid abounded also in small 

 orbicular points, constituting the ' molecular basis ' of the digestive product. In this worm it 

 is this fluid, and not the true blood, that is aerated ; the latter system is too little developed." 1 

 This quotation clearly shows that he was quite unaware the so-called " elliptical cells " are 

 always confined within the proboscidian sheath ; as well as points out the erroneous notion he 

 entertained of the true digestive tract, which in all cases can readily admit salt water (by mouth 

 or anus), if such be required, but certainly not for the purpose of converting it into " a vital 

 organized fluid." The proboscidian liquid and corpuscles, as I have previously shown, are very 

 far removed from sea-water, and hence have little analogy with the "chylaqueous fluid" so 

 frequently mentioned by investigators of the Invertebrates, 



4. The Aperture for the Extrusion of the Proboscis. 



This orifice is situated towards the ventral edge of the tip of the snout, and under favourable 

 circumstances in the living animal, may be seen as a terminal pore, surrounded by a closely set 

 series of radiating lines ; as, for instance, when the snout is bent upwards towards the tube of 

 the microscope (Plate X, fig. 16). The aperture has been called a genital pore by not a few 

 authors, e. g. (Ersted, Leuckart, and Quoy and Gaimard ; while others, such as Johnston, De 

 Quatrefages, Busch, Williams, and Girard, have interpreted it to be the mouth ; indeed, since the 

 proboscis was by many considered the alimentary organ, it could not be otherwise. It is 

 furnished with longer cilia from an early period; and in the adult these (cilia) form, when the 

 lips are slightly pouting, a very pretty arrangement (Plate XV, fig. 4, a c), similar to the 

 analogous opening in Lineus (Plate XIX, fig. 1). The striated ring surrounding this passage 

 in transverse sections of the tip of the snout (Plate X, fig. 1) indicates the special muscular 

 coat pertaining thereto. The canal (Plate XV, hg. 4, a b) proceeds straight backwards from 

 the aperture to a point in front of the commissures of the ganglia, where it meets the 

 differentiated walls of the proboscis (at a) ; and the cilia can be traced to this region, 

 but no further. The tube is simply hollowed out in the tissues of the head, and is 

 quite independent of the motions of the proboscis. It has a series of longitudinal muscular 



1 ' Philos. Trans./ part ii, 1852, p. 627, pi. xxxii, f. 25. 



