February 24, 192 1] 



NATURE 



845 



ordinary type automatically on the neighbouring 

 stand of Messrs. Creed and Co., Ltd. The Creed type 

 of printer was recently described in Nature (December 

 9, 1920, p. 472). The apparatus here exhibited is of 

 the improved form, in which the use of compressed 

 air is entirely done away with and a revolving type- 

 wheel takes the place of the lever typewriter 

 mechanism of the older apparatus. The main prin- 

 ciples of the selecting arrangement whereby the 

 Morse message is translated into type are the same. 

 The new instrument has a working speed of 175 words 

 per minute. 



The most complete line telegraph exhibit is that of 

 the Eastern and Associated Telegraph Companies, 

 which includes a complete set of apparatus as used 

 on a long cable circuit. This works with a Creed 

 printer of the older pattern used with the Muirhead 

 tvpe of receiving perforator. Among objects of his- 

 torical interest is an example of the original form of 

 the Kelvin siphon recorder. Attention may also be 

 directed to examples of different forms of relays used 

 in cable work and an example of an " electrolytic 

 magnifier," which is somewhat similar to a relay 

 except that instead of containing actual contacts that 

 are opened and closed by the galvanometer portion 

 of the apparatus, the moving pointer alters the rela- 

 tive position of wires dipping into an electrolyte, and 

 makes an alteration of resistance which affects the 

 balance of the duplex circuits and actuates the receiv- 

 ing apparatus accordingly. 



Recent advances in optical science are exemplified 

 by the exhibits of Messrs. Chance Brothers, Ltd. A 

 special feature is the demonstration of the properties 

 of "Crookes" glass for ophthalmic purposes, which 

 relieves the eves from strain by absoiT^ing the ultra- 



violet rays while allowing the whole of the visible 

 spectrum to pass. The company also exhibits for the 

 first time a new "daylight" glass, by the aid of 

 which colours may be matched by artificial light 

 exactly as in daylight. This is a glass of a bluish 

 tint which is- accurately balanced in colour against 

 the source of light to be used so as to absorb a selec- 

 tion of the rays and to allow a mixture to pass through 

 which approximates very nearly to daylight. The 

 problem is attacked in a different manner by the 

 Sheringham Daylight, Ltd., who show specially con- 

 structed reflecting shades which achieve a similar 

 result by reflection instead of by transmission. In both 

 cases the source of light employed is the half-watt 

 lamp. Another optical instrument which should not 

 be missed is the Optophone, which enables the blind 

 to read from ordinary type. This has already been 

 fully described in Nature (May 6, 1920, p. 295, and 

 August 5, 1920, p. 722), and is exhibited by Messrs. 

 Barr and Stroud, Ltd. 



A very comprehensive example of the methods of 

 modern medical research is presented by the display 

 arranged by the Middlesex Hospital, which includes 

 a large number of prepared sections relating to 

 parasites and bacteria mounted in microscopes. Ap- 

 paratus is also shown typifying the methods used 

 both for routine and research in photomicrography, 

 Rontgen-ray work, and various branches of bio- 

 chemical and physiological investigation. St. Mary's 

 Hospital Medical School has also an exhibit relating 

 to the part played by medical research in the promo- 

 tion of industrial efficiency. Among the subjects 

 illustrated are breathing apparatus for diving, mining 

 rescue work, and gas protection. Apparatus for the 

 recording of muscular effort is also shown. 



Human Tails. 



A'^ 



T a meeting of the Royal Anthropological Insti- 

 ■ tute held on February's, Dr. W. H. R. Rivers, 

 president, in the chair. Prof. Arthur Keith, in making 

 a report on a specimen of a human tail which had 

 been bequeathed to the institute by the late Dr. J. C. 

 McLachan, of Halifax, Yorks, took occasion to review 

 the present state of our knowledge regarding the 

 occurrence of true tails in human beings. The speci- 

 men submitted was a true human tail exactly similar 

 to one very completely examined by Prof. Ross Harrison 

 and described by him in the Johns Hopkins Hospital 

 Bulletin of 1901. Prof. Harrison's specimen, which 

 was removed from a boy aged six months, was 40 mm. 

 long at birth, 70 mm. long when excised, contained 

 striped muscle, and moved under various emotional 

 states. Dr. McLachan's specimen was removed from 

 a girl aged three months, measuring 105 mm. long 

 in its preserved state, 11 mm. in diameter at the base, 

 and tapering to a conical point. It also contained 

 strands of striped muscle, and must have had the 

 power of movement. As is the case in all such speci- 

 mens, with three recorded exceptions, no vertebrae 

 were present, nor could anv segmental arrangement 

 be observed in the central core. The .skin covering 

 the tail was studded with hair-roots and sebaceous 

 and sweat glands. 



Thanks to the labours of Keibel and Elze, and of 

 Prof. Streeter, of the Carnegie Institution, and of 

 his pupils, our knowledge of the development of a 

 true tail in' the human embryo may now be regarded 

 as complete. At the end of the fifth week of develop- 

 ment, when the human embryo is approaching 5 mm. 

 in length, caudal (post-sacral) segments begin to be 

 differentiated from the tail-bud represented by the 

 growing tip of the tail. Bv the beginning of the 



NO. 2678, VOL. ro6] 



seventh week, when the embryo is about 12 mm.»long, 

 the human tail reaches its maximum growth and 

 differentiation, there being then eight to ten caudal 

 segments within the projecting conical tail. In the 

 seventh week retrogression of the terminal and free 

 segments takes place, and towards the end of the 

 eighth week, when the foetus measures about 25 mm. 

 (i in.) in length, the surviving four or five basal or 

 coccygeal segments become submerged, drawing with 

 them the terminal atropic segments, the point of dis- 

 appearance of the terminal atropic part being marked 

 by a dimple. The caudal appendage which occa- 

 sionally occurs in children represents a persistence 

 of the terminal sep^mented part of the tail which 

 normally atrophies by the end of the eighth week. 



The disappearance of the tail from the bodv of man 

 is not a human, but a pre-human problern. It is 

 part and parcel of the wider problem of how and 

 when the upright, or, as Prof. Keith would prefer 

 to call it, the orthograde, posture was evolved. The 

 orthograde group of Primates is represented to-dav by 

 the gibbon, orang, chimpanzee, gorilla, and man; in 

 all of them the muscles of the spine, and of the thorax 

 and abdomen, and all the spinal and other nerve 

 reflexes which regulate the action of muscles, have 

 been transformed to suit the orthograde posture ; in 

 all of them the external tail has disappeared and 

 the basal or pelvic vertebrae of the tail have been 

 reduced to a coccygeal form. The tail is more vestigial 

 in the primitive small-brained gibbon than in man; it 

 is the discovery of a pre-gribbon stock which should 

 give us the history of the disappearance of the human 

 tail, and from the scant data at present available we 

 may infer that such a discovery is likely to be found in 

 strata lying well towards the base of Tertiary deposits. 



