194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Function of Swim-bladder.*— C. M. L. Popta gives an account of 

 a large number of experiments on this subject, and a full account of 

 previously recorded data, inferences, and opinions. She finds that the 

 swim-bladder favours the circulation of oxygen, and of gas in general, 

 in the body of fishes. This function is related to the needs of the 

 animal, and may be voluntarily controlled. The gases enter the cavity 

 by the blood-vessels, and pass out by the lymphatics. The organ in 

 question is not hydrostatic nor directly respiratory — it may have some 

 accessory uses, but its real function is to favour the circulation of gases. 



Structure and Function of the Saccus vasculosus in Fishes. f — 

 K. W. Dammermann has made a careful study of this structure, which 

 arises as a diverticulum from the posterior infundibular wall, and lies 

 with the hypophysis in the sella turcica. As has been repeatedly sug- 

 gested, the saccus vasculosus is not a gland, it is a sense-organ, and a 

 full account is given of its minute structure, its afferent and efferent 

 nerves, and its blood-supply. The organ is confined to Fishes, though 

 in higher Vertebrates there may be a representation of the recessus 

 posterior iufundibuli. The saccus vasculosus is probably homologous 

 with the infundibular organ of lancelets and the ciliated groove of 

 Tunicates. Dammermann argues ingeniously in support of the theory 

 that the saccus vasculosus enables the fish to become aware of the degree 

 ct oxygenation in the water, and thus to choose the most comfortable 

 depth. He proposes to call it a Benthic organ. 



Ventral Musculature of Fishes. J — K. Knauer has studied this in 

 various types. The simplest relations are in dog-fishes. There the 

 lateral trunk musculature is divided by four interstitial partitions, of 

 which the interstitium laterale is most conspicuous. But it cannot be 

 taken as the boundary between dorsal and ventral musculature, since 

 part of the muscle ventral to it is continued forwards to the skull, and 

 is undoubtedly dorsal. What is below the interstitium sublaterale is 

 ventral musculature. But this is only an indication of the general 

 nature of Knauer's investigation. 



Yawning in Fishes. § — Richard Elmhirst describes in cod, saithe, 

 cobbler, plaice, eel, and other fishes, an action like yawning, consisting 

 of a wide opening of the mouth, slow expansion of the buccal cavity, 

 erection of the gill-arches, followed by a rapid expulsion of the indrawn 

 water, most of which is emitted from the mouth, although some cer- 

 tainly goes through the gill-slits. This is often accompanied by a 

 distinct heaving of the pectoral region and erection of the pectoral fins, 

 and is quite different from the rapid movement of the operculum and 

 jaws, which is used to remove a foreign object, such as a bit of seaweed, 

 from the gills. From numerous observations, Elmhirst has been led to 

 think that this action of fishes is a real yawn, and serves the true phy- 

 siological purpose of a yawn, i.e. flushing the brain with blood during 



* Ann. Sci. Nat. (Zool.), xii. (1910) pp. 1-160. 



t Zeitschr. wiss. Zool., xcvi. (1910) pp. 654-726 (4 pis. and 1 fig.). 



I Arbeit. Zool. Inst. Univ. Wien, xviii. (1910) pp. 207-26 (3 pis. and 6 figs.). 



§ Zoologist, 1910, pp. 321-4. 



