316 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



atrophied condition of the proboscis itself and all its apparatus. It cannot be 

 affirmed, also, of the Nemerteans, that the fluid in the so-called blood-vessels is 

 devoid of corpuscles, for they occur in several species. Again, I think there can be 

 no doubt the fluid and discs exercise a very important influence on the reproduction 

 of the proboscis, a process hereafter to be described, as well as promote the absorp- 

 tion of the debris of the discarded organ when it happens to be included in the 

 chamber. But while thus affirming the fluid has a certain influence on, and bears 

 a certain relation to, the development of the proboscis, it cannot be said to be 

 indispensable for the appearance of the latter, since there is a small proboscis in 

 P. involuta, where the fluid is altogether absent. The views of Dr Thomas 

 Williams in regard to this corpusculated liquid, which he termed the ''chylaqueous 

 fluid," are so much at variance with accuracy, that I cannot pass them over in 

 silence. He says — " In the case of the Borlasiadae, Planiariadre, and Liniadae, the 

 chylaqueous fluid is contained in the digestive cseca and diverticula. In some of the 

 Planariadae, however, I have proved that a space does actually exist between the 

 digestive diverticula and the solid structure of the body, winch, is lined by a vibru- 

 tile epithelium, and into which probably the external water is in some way ad- 

 mitted. By this water, thus situated, the contents of the digestive Cieca are 

 aerated. The fluid oscillating in these cascal 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 organisation. 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."* The above clearly shows 

 that he was quite unaware that the so-called " elliptical cells" are always con- 

 fined within the cavity of the proboscidian sheath, as well as points out the errone- 

 ous notion he entertained of the true digestive tract, which in all cases can readily 

 admit salt water (by mouth or anus), if such is required, but certainly not for the 

 purpose of converting it into " a vital organised fluid." The proboscidian fluid and 

 discs, as I have previously shown, are very far removed from sea- water. 



In the Ommatopleans, the aperture for the extrusion of the proboscis is situ- 

 ated 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 IV. fig. 13). It is furnished 

 with longer cilia even in the young animal ; and in the adult these (cilia) form, 

 when the lips are slightly pouting, a very pretty arrangement (Plate VI. fig. \,a c), 

 similar to the analogous opening in Borlasia (Plate X. fig. 1). The striated ring 



* Phil. Trans. Part ii. 1852, p. 627, pi. xxxii. fig. 25. 



