September 17, 1891] 



NATURE 



483 



in length — the gills are no longer sufficient for purposes of re- 

 spiration, and the animals die in a very short time if prevented 

 fiom coming to the surface to breathe. (2) If tadpoles are 

 jirevented from using their lungs from an earlier stage onwards, 

 I he gills remain perfectly functional, and development proceeds 

 as usual. At metamorphosis, the fore-limbs are slow in becom- 

 ing free, owing to the retention of the operculum, that on the 

 same side as the spiracle appearing first. Eventually, a slit- like 

 spiracle is present on either side. In respiration, the mouth is 

 opened and closed, as in the tadpole. Specimens of branchiate 

 frogs were exhibited, in which the tail had shrunk to less than 

 half its original length. 



Exhibition of, and remarks upon, some young specimens 

 of Echidna aculeata, by Prof. W. N. Parker. The spe- 

 cimens are from the collection of the late Prof. W. K. Parker, 

 who received them from Dr. E. P. Ramsay, Curator of the 

 Australian Museum, Sydney. They are much curved towards 

 the ventral side, the snout pointing backwards, and the tail, in 

 I he older of the two stages, forwards. The younger stage 

 measures along the dorsal curve, from the end of the snout to 

 the tip of the tail, 12 cm., the greatest diameter of the body 

 being 3 cm. ; the corresponding measurements of the older 

 stage are respectively 21 "5 cm. and 6 cm. In the latter, the 

 body is covered with short scattered bristles. In both stages 

 tlie snout is very similar in form to that of Ornithorhynchus, 

 and is covered by a thick horny layer, but in other respects the 

 specialization characteristic of Echidna is already apparent. 

 The gape is narrow, and extends only a short distance down 

 the snout, and the manus, even in the younger stage, is already 

 much larger and stronger than the pes. The tail is short and 

 conical. There is no carimcle, or " egg-breaker," in the snout, 

 such as is seen in Ornithorhynchus. A few points in the struc- 

 ture of the fore-part of the head in the older stage were de- 

 scribed. The mouth has the narrow and tubular form seen in 

 the adult, and the long tongue has a horny tip. The glands in 

 relation with the mouth and nose are very numerous. There is 

 no trace of any teeth-rudiments, and in many other respects the 

 structure of the head shows extreme specialization. Jacobson's 

 organ is large, and highly developed. A well-marked " tur- 

 binal " is present in it. 



Prof. Plowes read a paper upon the classification of fishes by 

 their reproductive organs. On comparison of the urino-genital 

 organs of those Osteichthyes haying a non-abbreviated kidney 

 with the same organs of the higher Vertebrata and the Elasmo- 

 branchs, the female genital duct and the kidney are seen to be 

 inversely proportionate in length. No feature more fully cha- 

 racterizes the development of the Miillerian duct than the ac- 

 companying abbreviation of the kidney and the disappearance j 

 of its head segment. The persistence of the last-named among ! 

 the Osteichthyes, and its possible retention of the renal function | 

 in rare cases, taken in conjunction wiih the mode of develop- 

 ment of the ovary duct in these fishes, point to the conclusion I 

 that the latter is in no way homologous with the Miillerian duct 

 as ordinarily understood. Balfour's belief that the genital ducts | 

 are homologous in both sexes of the Teleosteans, is supported i 

 by the facts of anatomy ; and comparison of the reproductive j 

 system of the Ganoids with that of the Teleosteans shows { 

 the two to be modifications of the same common type ; and 

 the absolute structural community of the parts in the males 

 and females of the Sturiones, while further confirming Bal- 

 four's doctrine, is opposed to Jungersen's implication that | 

 the subtle differences in the mode of development of the 

 ducts in the opposite sexes of the Teleostei, are indicative of 

 their non-homology. The facts above alluded to justify us in 

 regarding the genital ducts of the Osteichthyes, not only as 

 homologous in the two sexes, and primarily independent of the 

 genital glands, but as distinct structures sui generis, probably 

 unrepresented in all other Vertebrates. The Plagiostomi and 

 Holocephali, in which vasa eflferentia are present and the kid- 

 ney becomes an accessory to reproduction in the male, may be 

 grouped together into a Nephrorchidic Series, as distinguished 

 Irom an Enlhorchidic Series, embracing the Ganoids and Tele- 

 osteans. Comparison of the pori genitales in relation to the 

 coalesced ureters of the Marsipobranchii with the corresponding 

 parts of the females of those Teleostei destitute of genital ducts, 

 especially in consideration of the facts concerning the develop- 

 ment of the parts recorded by Scott, Liszt, and others, supports 

 Rathke's conclusion that the ancestors of the former fishes must 

 have possessed genital ducts. The Osteichthyes, although spe- 

 cialized in respect to many features of their organization, have, 



NO. 1 142, VOL. 44] 



together with the Marsipobranchs, retained the least modified 

 type of urinogenital organs known for living Vertebrates. W. 

 N. Parker's recent and important discovery that, while in 

 Protopterus a Miillerian duct is present, vasa eflferentia are 

 absent, and the testicular products are discharged through a duct 

 more nearly comparable to that of the bony fishes than to the 

 genital ducts of any other Vertebrates, suggests that the deve- 

 lopment of vasa efferentia and the assumption of a genital func- 

 tion by the Wolffian duct may have been eflfected subsequently 

 to the formation of the Miillerian oviduct. And further com- 

 parison of the Dipnoi with the Elasmobranchii suggests that 

 the former may have struck off from the Holocephalic branch of 

 the latter before the diflferentiation of the ancestors of its living 

 members. 



Another paper by Prof. Howes dealt with the customary 

 methods of describing the gills of fishes. The gills of Plagio- 

 stomes and Marsipobranchs 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 

 nomenclature for the parts concerned. The facts of develop- 

 ment show : (i) [on the assumption that the mandibular or 

 mouth cavity is serially homologous with a pair of post-oral 

 visceral clefts] that each gill lies in front of its corresponding 

 skeletal arch ; (2) that the saccular type of gill met with in the 

 Marsipobranchs and Plagiostomes is that from which the pec- 

 tinate one of the higher gnathostomatous fishes has been derived ; 

 and (3) that a mandibular gill has no existence in living fishes. 

 Gills of the Marsipobranch-Plagiostome type may be conve- 

 niently described for general anatomical purposes, as Cysto- 

 branchicE, and those of the higher Telosteoid type, as Pectino- 

 branchiix ; while the paits of the individual gills themselves 

 should be in all cases enumerated in relation to the visceral 

 pouches from which they arise. Thus, the spiracular gill of 

 Eiasmobranchs (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 of Dohrn 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 pos- 

 sibility that these filaments may (at any rate for the most part) 

 represent mandibular gills of a reversional character must not be 

 overlooked. 



Dr. Arthur Robinson communicated some facts relative to the 

 development of the rat and the mouse. The most important 

 part of the paper dealt with the relation of the yolk sac to the 

 maternal tissues. The crypt in the uterine wall which lodges 

 the ovum becomes shut off from the rest of the cavity of the 

 uterus by a fusion between the distal proximal walls of the 

 uterus. The greater part of the space so formed is occupied by 

 the ovum ; the remaining portions are converted into maternal 

 blood sinuses ; the blood in these sinuses bathes the trophoblast 

 and the distal end of the yolk sac. Later, the distal part of the 

 yolk cavity is obliterated by the apposition of its walls, but the 

 proximal portion remains ; diverticula grow out from from this 

 into the placenia, which maintain the iniimate relation of the 

 yolk sac to the maternal blood. It seems probable, in view of 

 these facts, that the yolk sac plays an important part in the 

 nutrition of the foetus. The allantois is a solid mass of meso- 

 blast containing no diverticulum from the alimentary tract, and 

 does not become attached to the trophoblast until comparatively 

 late in the life of the embryo, i.e. the eleventh day. 



Another paper by the same was entitled " Observations upon 

 the Development of the Spinal Cord in Mtis tnusculus and Mus 

 dccumanus: the Formation of the Septa and the Fissures." The 

 anterior and posterior septa of the cord were stated to be formed 

 by the spongioblasts of the cord itself, and not by ingrowths of 

 the enveloping sheath of pia mater. 



Prof. Marcus Hartog communicated an outline classification 

 of sexual and allied modes of protoplasmic rejuvenescence. 



I. The following modes of rejuvenescence occur in cellular 

 and in certain apocytial organisms : — 



A. Plastogamy : the fusion of cytoplasta into aplasmodium, 

 the nuclei remaining free. 



