790 MECHANISM OF RESPIRATION, ETC. 



When an Octopus is observed at rest, attached by its suckers to a surface, its violent 

 respiratory movements are seen to depend upon the muscularity of the mantle and funnel, 

 the expansion of the mantle being synchronous with the contraction of the funnel, so 

 that while fresh sea-water is entering the mantle-cavity in order to bathe the gills, water 

 which has completed its work of oxygenation is being expelled through the funnel. 

 In the case of Nautilus the thin transparent mantle is closely applied to the inner surface 

 of the mouth of the shell, and takes no part in promoting the respiratory current of 

 water. The incurrent and excurrent streams are alike caused by the rhythmic con- 

 tractions of the funnel, more particularly of the alae infundibuli. 



This is an interesting difference between the mechanism of respiration in Nautilus 

 and Dibranchs respectively, and was noted by me in 1896 {Quart. J. Micr. Sc. Vol. 39) in 

 correction of a statement by Moseley, who attributed breathing-movements to the mantle 1 . 

 The funnel of Nautilus is thus the essential organ of locomotion and the principal ac- 

 cessory organ of respiration, a combination of functions which should not be dissociated 

 from its anatomical structure and relations when its morphology is under discussion 2 . 



It is not my intention to describe in detail the renal and pericardial follicles 

 which adhere respectively to the anterior and posterior walls of the afferent branchial 

 vessels, the former enclosed within the renal sacs and the latter projecting into the 

 pericardium. 



The pericardial glands discharge a fluid excretory product into the pericardium, 

 which has been met with as a tenacious coagulum by Keferstein (1865) and Haller (1895), 

 but I have no record of this. The excretion of the renal glands, as is well known, 

 consists of solid concretions with concentric stratification somewhat as in starch-grains 

 (PL LXXVI. fig. 2). They are said to consist mainly of phosphates (Blasius, Keferstein). 

 When seen in bulk, filling the cavities of the renal sacs, their colour varies from white 

 through scarlet to deep crimson (cf. PL LXXV. and LXXVI. fig. 1). I can suggest no 

 explanation of this variation in colour of the excretory products. The colour is retained 

 in many of my alcoholic specimens. 



A dissection displaying the afferent and efferent vessels of the larger gill of the 

 right side is represented on PL LXXXII. fig. 8, to the explanation of which I may refer 

 the reader. 



Both the renal and the pericardial follicles are contractile in their entirety, the 

 systole of the heart synchronising with the diastole of the pericardial glands and with 

 the systole of the renal organs 3 . 



With regard to the branchial sense-organs or osphradia which are highly charac- 



1 Moseley, H. N., Notes by a Naturalist on H.M.S. Challenger, 2nd edit. 1892, p. 257. " On either side 



the fold of mantle closing the gill cavity was to be seen rising and falling, with a regular pulsating 



motion, as the animal in breathing took in the water, to be expelled by the siphon." The "fold of mantle" 

 is really the ala infundibuli. 



2 The mechanism of respiration of the Cephalopoda was dealt with in an instructive and suggestive 

 manner by Williams, T., " On the mechanism of aquatic respiration and on the structure of the organs of 

 breathing in invertebrated animals. Cephalopoda." Ann. Nat. Hist. (2) xix. 1857, pp. 193 — 201, PI. xv. He 

 points out the analogy between the contractile gills of Cephalopoda and the systole and diastole of the lungs 

 in pulmonary respiration. 



3 I also observed rapid independent contractions of the renal organs. 



