NATURE 



\_N0V. 22, il 



to displace the beam in a definite manner, than upon the magni- 

 tude of the displacement so p-oduced. As in other instruments 

 whose operation depends upon similar principles, e.g. galvano- 

 meters, it is useless to endeavour to increase the sensitiveness by 

 too near an approach to instability, becau-e the effect of casual 

 disturbances is augmented in the same proportion as that of the 

 forces to be estimated. If the time of vibration be halved, the 

 displacement due to a small excess of weight is indeed reduced 

 in the ratio of four to one, but it is not necessarily rendered 

 any more uncertain. The mere diminution in the amount of 

 displacement may be compensated by lengthening the pointer, 

 or by optical magnification of its motions. By the method of 

 mirror reading such magnification may be pushed to almost any 

 extent, but I am dealing at present only with arrangements 

 adapted for ordinary use. 



In the balance (by Oertling) that I am now using, the scale 

 divisions are finer than usual, and the motion of the pointer is 

 magnified four or five times without the slightest inconvenience 

 by a lens fixed in the proper position. The pointer being in the 

 same plane as the scale divisions, there is no .sensible parallax. 

 In this way the advantage of qnick vibrations is comb'ned with 

 easy visibility of the motion due to the smallest weights appreci- 

 able by the balance. 



To illuminate the scale, the image of a small and distant gas 

 flame is thrown upon it by means of a large plate-glass lens. 

 This artificial illuminatio'i is found to be very convenient, as the 

 instrument stands at some distance from a window, but it is not 

 at all called for in consequence of the use of the magnifying 

 lens. 



ON THE DEVELOPMENT OF PERIPATUS'^ 

 A MONG the acquisitions I made during my journey to the 

 ■^ West India Island of Trinidad, a rich collection of Peri- 

 patus stands in the first rank. This has put me in a position to 

 correct many mistakes, and to contribute a good deal to the 

 knowledge of the histological anatomy of this interesting animal 

 form, as well as especially to follow the process of development 

 from beginning to end. Postponing for the present the anatomy 

 of the adult animal, inasmuch as we have on this subject a good 

 many studies, some of which are very good (for instance, that of 

 Gaffron in Zool. Beitriige, edited by Dr. A. Schneider), I shall 

 confine myself to a preliminary notice of the earliest stnges of 

 the development of Peripatus, although my investiijations have 

 not as yet been brought to a conclusion, nor have I been able to 

 devote any attention to the development of the organs. I do 

 this chiefly because the treatise published by Moseley and Sedg- 

 wick from the posthumous notes of Balfour contains some re- 

 presentations of embryos and cro:s-sections of the same, upon 

 whose accuracy in details I, with my rich and well preserved col- 

 lection of specimens, and observations on fresh objects, must 

 cast some doubt, and the interpretation of which does not bear 

 investigation. And yet these already serve as evidence for some 

 theoretical explanations of embryonic processes in other groups 

 of animals, which it would be well to avoid in such a case. 



I collected in Trinidad over a hundred specimens of Peripatus 

 Ehaardsii, and a small number of a new species which is dis- 

 tinguished by its size from all those hitherto known, and which 

 may briefly be thus characterised : The females, which are con- 

 siderably larger than the males, attain a length of 15 cm. and a 

 diameter of 8 mm.; the males gro.v to a size of about 10 cm. Their 

 colour is a plain reddish bro\\n above, darkening a little towards 

 the middle line of the back, and growing pale a little towards 

 the sides. The head, or, more correctly, the fnehead, as well 

 as the antenna;, is black, and marked off on the dorsal side by 

 a light yellow necklace, which is often slightly interrupted in the 

 middle, from the rest of the body. The under side is of a dark 

 flesh colour. This species is especially characterised by possessing 

 forty-one to forty-two pairs of feet, which is the highest recorded 

 number, and a number which differs greatly from that of all 

 other species. I call this new species Peripatus lorqiiatiis. 



The ovaries are two small, elongated bidics, which are gene- 

 rally united along their whole length, and so appear as a narrow, 

 spindle-shaped body, which is connected by one or often by two 

 delicate muscular threads to the body wall. The ovaries are 

 prolonged into the two horns of the uterus, which, each forming 

 a bow with several curves, unite immediately before reaching 

 the genital pore to form a very short vagina. At the point where 



' Trp.nsl.ited from a nolice, by Dr. J. von Kennel of Wurzburg, in the 

 I ogischcr Anzelgcrlix OaohnZ, 1883. ,lUi. 



the ovaries pass ever into the uterus is situated a small, nipple- 

 shaped gland and a spherical reeeptaculum seminis, the orifice 

 of v\hich every egg has to pass before it can enter the uterus. 

 Now as a large number of embryos, from the "just furrowed " 

 egg to the matured young, are always found in the uterus, it is 

 very probable that each female Peripatus is only fertilised once. 



The eggs of Peripatus contain no yolk, and seeing that in 

 spile of this an animal of half the length that it attains when adult 

 develops itself in the uterus out of a small egg whose diameter 

 is about c'04 mm., there mu-t be some quite peculiar means 

 for its nutrition, and this is the case to the most astonishing 

 extent and in the most surprising manner. 



As soon as the fertilised egg enters the thin portion of the 

 uterus, a smill enlargement takes place in its lumen, which is 

 very narrow and is surrounded with very deep cylinder epithelia. 

 Simultaneously with this the epithelium cells mass themselves a 

 little together ; the furrowed egg settles upon the epithelium, 

 and immediately the lumen widens a good deal by the epithelial 

 cells of the uteru; becoming very depres.sed at that spot ; so 

 flattened do they become that they form a very thin pavement- 

 epithelium, whereas before and behind the "breeding-nidus" 

 (Bnithele) an embankment is formed by the thickening of the 

 connective tissue of the uterine walls, so as nearly to fill up 

 the u'erine canal. 



In this stage we find a hemispherical mass of homologous 

 cells attached by a broad basis to the extraordinarily thin 

 lining of the uterine cavity, a lining which has been formed out 

 of the two cells that originally .surrounded the egg. Presently a 

 small depression develops in this hemispherical mass, and now 

 the embryo forms something like the half of a hollow sphere, 

 still consisting of but a few cells. Through the multiplication 

 of these the hemisphere and the cavity in it become a little 

 larger, and now a difference is perceptible between the cells of 

 the embryo which are situated immediately upon the uterine 

 epithelium and the rest. The former, which I shall for brevity's 

 sake here call basal cells, have a long, narrow, and very com- 

 pact nucleus, whereas the others have a large, circular, granular 

 nucleus. The basal cells multiply, and in doing so close the 

 opening of the hemisphere, and form a layer which, lying between 

 the embryo and the uterine epithelium, fastens the former to the 

 latter. In the meantime the cells of the hemispherical mass have 

 also multiplied to such a degree that the side looking towards 

 the lumen of the uterus appears thickened by the cells mutually 

 displacing each other. 



In this st.nge the » hole condition of the embryo'resembles that 

 of a flattened hollow sphere whose free wall has been thickened ; 

 thelonger diameter is 009 mm., and the lesser O'oymm. The basal 

 cells of the embryo now spread themselves out a little, a few 

 isolated ones come out from under the embryo, and thus enlarge 

 the basis of attachment — they form an embryonic placenta. From 

 them is also developed a very delicate membrane, which becomes 

 closely applied to the uterine epithelium, and envelops the 

 embryo — it may be shortly designated as amnion. 



In the meanwhile changes are also going on in the uterus ; 

 the epithelium of the "breeding-nidus" has become a little 

 thicker, the nuclei have increased in number, and a number of 

 small dark brown pigment granules have developed and col- 

 lected in the protoplasm of the flat cells, which for a long time 

 mark off sharply the uterine epithelium from the embryonic 

 portions. 



The basal cells now multiply to a remarkable extent, partly so 

 as to increase the size of the phcenta, and partly in a direction 

 perpendicular to it, forming a solid stalk upon which the embryo 

 is pushed out free int) the lumen of the "breeding-nidus." The 

 whole now forms a pyriform mass ; the little head of the pear, 

 the actual embryo, is, however, now no longer hollow ; cells 

 have been thrust in from the side furthest away from the staH;, 

 which have filled up the whole "furrow cavity " ; a sharp limit, 

 however, is visible between them and the ectoderm at every 

 ]ioint except the place w-here they have been invaginated ; 

 this point, which is comparable to the bla-topore of other 

 emViryos, persists for a long time as the spot where material for 

 the inner germinal Layers is being continually provided by in- 

 vagination, and is still demonstrable in embryos in which the 

 form of Peripatus has long since been recognisable. 



As soon as the "furrow cavity" has been filled up in the 

 manner that has been described, a new cavity develops by 

 fission in the central mass of cells. This is the definite visceral 

 cavity. It develops by the embryo becoming composed of two 

 layers (ectoderm and entoderm) in the half that is nearest to the 



