HARDVVICKE'S SCIENCE-GOSSIP. 



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NOTES ON SOME COMMON SEA-SLUGS. 



By Dr. P. Q. KEEGAN. 



\Co>tti)aicd froi7i page 195.] 



!?• ME nervous system 

 of the Eolidoe is 

 in many respects 

 similar to that of 

 the DoridiE already 

 indicated ; the 

 cerebral ganglia 

 are large, there are 

 ganglia at the base 

 of the tentacles 

 supposed to be 

 olfactory in func- 

 tion, and there is 

 a large nerve 

 which passes from 

 the cheeks to the 

 glands of the dor- 

 sal papillae. The 

 organs of circula- 

 tion are rather 

 simple, consisting 

 of a heart with an auricle and ventricle furnished with 

 valves and arteries and veins, some of which latter 

 accompany the papillae ; but be it observed that the 

 latter have no apparent branchial veins in connection 

 with them. Respiration is performed by the entire 

 surface of the skin, which (including the papillce) is 

 the theatre of incessant ciliary movement. But per- 

 haps the most interesting anatomical features observ- 

 able in this family are the digestive organs, and we 

 shall therefore specify their various constituents in 

 detail. An outer and an inner lip lead to the cheeks, 

 which are composed of two horny plates with strong 

 cutting edges, and enclose a spiny tongue adapted for 

 grasping food, and furnished with strong muscles 

 fitted to enact the necessary movements ; from the 

 hinder portion of the mouth a short narrow throat 

 passes backwards ; and thereon follows a pear-shaped 

 stomach, having a wide extension to the rear, from 

 which branches and tiny tubes extend into the dorsal 

 papillK, becoming a more or less complicated and 

 developed apparatus for the secretion of the bile, and 

 •whence they are continued into ovate vesicles charged 

 No. 214.— October 1882. 



with poison-darts or thread-cells, which are vented 

 forth from an opening at the extreme end of the 

 papilla ; from the hinder portion of the stomach a 

 short intestine passes off and ends in an anus at the 

 right side of the body. 



As these papillae are the most conspicuous and 

 interesting organs discernible in the Eolidce, let us 

 perform an experiment in order to demonstrate their 

 structure. Here before us is a choice specimen of 

 Eolis Drmnmondi, waving and flaunting and "drib- 

 bling " about in this crystal vase of sea-water. His 

 back quivers with an array of ever-mobile lances, 

 which, when the body is touched, instantly bristle up 

 " like quills upon the fretful porcupine," and curl 

 over towards the point of irritation. Now with a fine 

 pair of scissors let us clip off one of these striped and 

 white-tipped filaments, and covering it on a slide 

 with a piece of thin glass, let us first inspect it with 

 a hand-lens. We now perceive in the centre of the 

 organ a straight reddish-brown canal filled with what 

 seems lighter and denser vesicular or granular matter 

 to near the tip, and then it winds about and seems 

 to enter an ample oval chamber of an opaque-white 

 colour. Placing the slide now under a J-inch ob- 

 jective, what do we see ? We see a central yellowish 

 canal with its walls slightly waved so as to form little 

 receptacles or follicles, and lined with a number of 

 yellowish or reddish-brown (burnt sienna) coloured 

 globules or accumulations, which seem to be filled 

 with or composed of an oily material, of a lighter or 

 a darker tint. These vesicles seem not to be fixed, 

 but they move about within the gland under the 

 influence of pressure, and they are accumulated in 

 irregular clusters or "mulberry masses" of every 

 shape and size. In some of the species, when these 

 globules are viewed under very high powers, they are 

 seen to be composed of rounded and nucleated granules 

 of various dimensions. These gland-cells secrete thi 

 bile from the minute blood-vessels which we now see 

 environed with the longitudinal and circular muscular 

 fibres which so thickly throng the space between the 

 wavy wall of the gland and the external walls of the 

 papilla. Passing the slide now, so as to view the 



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