386 



NATURE 



\_Augtist 8, 1878 



sions and eccentricity of the orbit of the comet are 

 now : — 



Perihelion distance ... I '3393 | Semi-axis major ... 2*9956 



Aphelion ,, ... 4"65i8 j ,, minor ... 2'^g6i 



Eccentricity ... 0*55289 



The interval between the perihelion passages in 1873 

 and 1878 is 189978 days. 



BIOLOGICAL NOTES 



The Primary Germ-Layers and the Origin of 

 THE Male and Female Reproductive Elements. — 

 Prof. Edouard Van Beneden, of Li^ge, three years ago 

 observed that in the marine hydroid polyp Hydractinia 

 the cells forming the testis and giving rise to spermatozoa, 

 were derived from an ingrowth of the outer of the two 

 primary cell-layers which form the foundation of all 

 higher animal bodies, whilst the ova, he found, were 

 simply cells of the inner primitive layer. This com- 

 plementary function of the ectoderm and endoderm in 

 Hydractinia led him to frame the hypothesis that 

 throughout the animal kingdom the outer cell-layer is 

 male in function, and the inner cell-layer female. Cn 

 reviewing the facts known as to the derivation of the 

 sexual cell-elements in various groups of animals, he was 

 able to show a considerable amount of evidence in favour 

 of the view that the testis is always ectodermal and the 

 ovary always endodermal. Though accurate obser- 

 vations in this matter are excessively difficult, and 

 definite knowledge as to the facts, in nearly all cases, 

 is still wanting, yet Prof. Van Beneden's hypothesis 

 was plausible and worthy of full consideration. It 

 has been adopted by Gegenbaur in the last edition 

 of his " Grundriss." The hydroid polyps consisting, as 

 they do for the most part, of the two primary cell-layers 

 in a very slightly differentiated condition, present the 

 most ready field for the further testing of Van Beneden's 

 hypothesis. The observations of Kleinenberg on Hydra 

 were opposed to it. According to these boih the sperm- 

 cells and the egg-cells of Hydra develop from the ecto- 

 derm. Mr. J. Ciamician, of Vienna, has made a special 

 study of this question in certain genera of hydroids 

 {Zeitsch. wiss. Zoologie, 1878, part 4), and has published 

 careful drawings in support of his statements. In Tnbu- 

 laria mese7nbryanihe7num, assuming the accuracy of Mr. 

 Ciamician's drawings, both female and male reproductive 

 cells develop from a hollow in-growth of the ectoderm (the 

 gonophors of the two sexes being distinct), which at first 

 depresses the endoderm, but is afterwards itself flattened 

 out by the up-growth of the endodermal layer of the 

 spadix. In Ktideiidrhim ramosum the ova develop from 

 cells of the ectoderm, and the sperm-cells from cells 

 of the endoderm, precisely the reverse of the relations 

 detected by Van Beneden in Hydractinia. It seems 

 hardly possible to interpret Mr. Ciamician's drawings of 

 Eudendrium in any other sense than that which he 

 himself adopts ; the cell-layers at all stages are as 

 clear in this species as they possibly can be. In the 

 female gonophors of Hydractinia, Van Benedeti saw an 

 in-pushing of ectoderm at the apex developed in the 

 same place as the in-pushing at the apex of the male 

 gonophor, from which the sperm-cells developed. Van 

 Beneden interpreted the rudimentary in-pushing in the 

 female gonophor as a survival of a primitive hermaphro- 

 dite condition of the gonophors. Ciamician considers, 

 on the contrary, that this ectodermal in-pushing is only 

 the commencement of the formation of a medusa (in fact, 

 the_ space between umbrella-margin and manubrium), 

 which, instead of being completed, subsides into the con- 

 dition of a medusoid gonophor. Hence, in place of a 

 constant law of ectoderm being male and endoderm 

 being female, we have in the three genera Tubularia, 

 Hydractinia, and Eudendrium, the following variations 

 respectively :— i, ectoderm male and female ; 2, ectoderm 



male, endoderm female ; 3, ectoderm female, endoderm 

 male. The only possible generalisation from these facts 

 is that of Ciamician, viz., that primitively the sexual 

 functions are not assigned exclusively to cells of either 

 layer : ectoderm may produce both male and female 

 elements, and so may endoderm. With increased deve- 

 lopment and specialisation of structure, the production 

 of reproductive elements would become limited to particu- 

 lar tracts of cells, and these would be necessarily either 

 exclusively endoderm-cells or exclusively ectoderm-cells, 

 but might be either one or the other indifferently even in 

 closely-allied genera ; and might be the same or comple- 

 mentary for the ovary and testis respectively. Neverthe- 

 less it must be admitted that though such indefiniteness 

 in the relation of the sexual glands to the primitive cell- 

 layers might be expected in Coelentera where the dif- 

 ferentiation of the two layers is at its commencement 

 (both layers, for instance, developing nematocysts), yet in 

 the higher groups of the animal kingdom we should be 

 justified in looking for absolute constancy in the deriva- 

 tion of ovary and testis respectively from one or other 

 (the same or diverse) of the two cell-layers — and we have 

 not ground for supposing that this derivation would be 

 the same in each of the great phyla until we can show 

 that it is more constant in the Vermes than in the 

 Coelentera. E. R. L. 



The Toilet Habits of Ants. — The Rev. H. C. 

 McCook, of Philadelphia, eulogises the neatness of the 

 agricultural ant, as observed in confinement at any rate. 

 The most minute particles of dirt are carefully removed, 

 and the whole body is frequently and thoroughly cleansed, 

 especially after eating and sleeping. They assist each 

 other in the general cleansing, and the attitude of the 

 ant under operation is one of intense satisfaction, like 

 that of a family dog being scratched, a perfect picture of 

 muscular surrender and ease. Mr. McCook has seen an 

 ant kneel down before another, and thrust forward the 

 head under the face of the other, and lie motionless, ex- 

 pressing quite plainly the desire to be cleansed ; the other 

 ant understood this, and went to work. Sometimes this 

 is combined with acrobatic feats, in Mhich these ants 

 excel, jumping about and clinging to tlades of grass in a 

 remarkable fashion. Sometimes the cleansing ant hangs 

 downward from the grass, and to her the ant operated 

 upon clings, reaching over and up with great agility to 

 submit to her friend's offices. Evidently moisture from 

 the mouth is used for washing. Mr. McCook has observed 

 most minutely the whole of these processes, which are 

 recorded in the Philadelphia Academy's Proceedings for 

 this year. He suggests that with ants as with the human 

 kind an artificial condition induces greater attention to 

 personal appearance. 



The Mode of Recognition among Ants. — The 

 combats and communications of ants are among the 

 most interesting and mysterious phenomena. The Rev. 

 H. C. McCook has given an account to the Academy of 

 Natural Sciences at Philadelphia of some experiments 

 he has made to determine what is the mode of recognition 

 among ants. He has studied the pavement ants {Tetra- 

 moriiim caspituin), which he has observed engaged in 

 continued combat for over a fortnight, the warriors being 

 only the workers or neuters. There is no distinguishable 

 difference between the ants of the fighting parties, yet 

 they recognise each other infallibly as friend or foe. 

 They challenge all comers with their antennae ; if they 

 are friends, they pass on ; if foes, they straightway inter- 

 lock and "fall to." Sometimes many ants are congre- 

 gated against one, which is being torn limb from hmb. 

 Mr. McCook surmised that recognition was based upon 

 a certain odour emitted by the respective factions. He 

 found that if they were enveloped in an odour of eau-de- 

 Cologne, while not at all deprived of activity, all becanie 

 harmonious ; those who were previously engaged in 



