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XVIII. — Notes on the Anatomy of the Genus Firola. By John Denis Macdonald, 

 R.N., F.R.S., Surgeon of H.M.S, " Icarus." Communicated by Professor 

 Maclagan. (Plate IX. fig. 4.) 



(Read 5th January 1863.) 



In a successful haul of the towing net, off the Island of Sardinia, I obtained a 

 very beautiful Firola, which gave me a good opportunity of testing the truth of 

 my former conclusions with regard to the economy of the Heteropoda in general, 

 and of Firola in particular ; and I have great pleasure in submitting the facts 

 arrived at, with the accompanying enlarged figure of the visceral nucleus and 

 the neighbouring parts, to the Royal Society of Edinburgh, as an appendix to 

 my paper " On the Anatomy and Classification of the Heteropoda," already 

 brought under its consideration.* 



I find that the relationship between Firola and Firoloides is even closer than 

 I had originally imagined, and with the exception of the presence of gills in the 

 former genus, nearly every anatomical point occurring in one may be distinctly 

 traced out in the other, only differing in relative characters. 



To avoid unnecessary repetition, I shall simply explain the accompanying 

 figure, and enlarge in passing upon any matters of importance that may suggest 

 themselves. 



Explanation of Plate IX. fig. 4. 

 a. Integument. 



6. Muscular sheath. 



c. Visceral nucleus, including the stomach, intestines, liver, testis, &c. 



d. Vesicula seminalis. All these organs are invested by an oval capsule, with its long diameter 



directed obliquely downwards and forwards, having the stomach at the lower end, and 

 the trumpet-like vent above, and in front, lying in relation to the Sinus-system, the heart, 

 great vessel, and oesophagus. 



e. Seminal opening. 

 /. Intestine. 



g. Anal orifice, plicated internally, and richly ciliated. 



h. Gills, with their zig-zag folds, giving the organs a pinnate appearance, which is often in- 

 correctly given in figures of the Heteropoda. 



i. Ciliated fossa fronting the gills, the cilia disposed in a circular band, and undulating in 

 the direction of the arrows. 



k. Sinus-system, communicating directly with the auTicle of the heart ^n), and everywhere 

 intersected with muscular bundles and fibres. 



/. Circular opening, leading into what I have been induced to regard as an inverted mantle- 

 cavity, whose walls are much lobulated and highly contractile, so that the sea-water 

 is ejected through the opening which is guarded by a sphincter. A vis e fronte effect 



* Trans. Eoy. Soc. Ed., vol. xxiii. p. 1. 

 VOL. XXIII. PART II. 3 G 



