702 REPORT— 1891. 



Like Professor Allman I must deny the possession of blood-vessels, or that the 

 * Haus ' has any respiratory function, although I must admit there were some 

 grounds for Von Mertens' idea in the very perceptible systole and diastole seen in 

 the thickened laminae of the horns of the mitre, in apparent response to the vibra- 

 tion of the tail. By this means the water contained in the envelope was con- 

 stantly renewed, and the ova therein protected duly oxygenised. 



I feel quite certain that this is the main function of this ' Haus,' and that Dr. 

 Allman was correct in calling it a nidamental covering for the ova, for in the en-' 

 velopes of both my specimens were ova to be seen, while in those of Dr. Allman 

 there were young Appendicularise. 



This sac is probably a primitive test, resembling the transparent test of Clarelina, 

 and this supports the idea of Professor Herdman that the Appendicularise were an 

 early offshoot from the ancestral chordate form. In the Appendicularia there is 

 no separate peribranchial cavity within which the ova can be fertilised and 

 developed. 



This envelope is only loosely attached to the animal's body, for in the struggle 

 of the creature to get away from the strong light thrown upon it by the micro- 

 scope it made a most vigorous contraction, and thereby jerked itself free from the 

 membrane, leaving it behind in a limp, collapsed condition, without apparent 

 vitality of any kind. 



8. On the Gustomary Methods of Describing the Gills of Fishes. 

 By Professor G. B. Howes, F.L.8., F.Z.8. 



The gills of Marsipobranchs and Plagiostomes are not unfrequently enumerated 

 in relation to the opposite walls of the visceral sacs which give origin to them, 

 while those of the higher fishes are enumerated in relation to the opposite faces of 

 the septa which bear them. The confusion arising out of this is well known to 

 teachers, and is in itself sufficient to justify the introduction of a revised nomen- 

 clature for the parts concerned. The facts of development show (i.) (on the 

 assumption that the mandibular or mouth cavity is serially homologous with a 

 pair of post oval visceral clefts) that each gill lies in front of its corresponding 

 skeletal arch ; (ii.) that the saccular type of gill met with in the Marsipobranchs 

 and Plagiostomes is that from which the pectinate one of the higher gnathosto- 

 matous tishes has been derived, and (iii.) that a mandibular gill has no existence 

 in living fishes. Gills of the Marsipobranch-Plagiostome type may be conveniently 

 described for general anatomical purposes as Ci/atobrancJiia;, and those of the 

 higher Teleosteoid type as FectinobrancMm ; while the parts of the individual gills 

 should be in both and in all cases enumerated in relation to the visceral pouches 

 from which they arise. Thus, the spiracular gill of Elasmobranchs (often termed 

 the mandibular pseudobranch) should be described as the hyoid hemibranch, and 

 the opercular gill of the higher fishes (often termed the hyoid pseudobranch) as 

 the first branchial hemibranch. 



The well-known series of buccal filaments met with in certain Chelonia appear 

 to have the fundamental relationships of gill folios, and in view of the discovery 

 by Dohrn, Piatt, and others that the buccal sac would appear, from its mode of 

 development in the Teleostei, to be the morphological equivalent of a pair of gill 

 pouches, the possibility that these filaments may (at any rate for the most part) 

 represent mandibular gills of a reversional character must not be overlooked. 



9. Exhihition of a very small Parrot from the Solomon Islands. 

 By Canon Tristram, F.B.S. 



