1891.] MICEOSCOPICAL JOURNAL. 65 



bodies. A dip may be made widi the tube, and the drop examined un- 

 der the microscope in a shallow cell, when an immense number of 

 pear-shaped bodies, having a red spot somewhere about them, will be 

 seen in rapid locomotion. No means whereby this motion is accom- 

 plished are visible. If a most minute dose of a solution of osmic acid 

 be allowed to absorb itself under the cover-glass, by putting the drop 

 of solution on one side of it, and a small piece of blotting-paper on the 

 other, as it abstracts the water it allows the osmic acid solution to take 

 its place. This almost instantly kills the protococcus, and soon it be- 

 gins to assume a darkened appearance, when its small end, two long 

 slender filaments, will be seen, which, lashing the water, propel the 

 alga along. The osmic acid may now be withdrawn by the same 

 method by which it was introduced, distilled water taking its place. 

 There will always be enough of the osmic acid left in the fluid to act as 

 a presei'vative, when the cover-glass may be cemented down. 



\_To be continued.'] 



The Significance of Sex.* 



By henry L. OSBORN, 



HAMLINE, MINN. 



There is, perhaps, no more noticeable nor less intelligible fact in bio- 

 logical science than sex. Except among the lowest living things, espec- 

 ially in the animal kingdom, two living beings, more or less alike, yet 

 more or less unlike, must co-operate in order to the perpetuation of the 

 species. The fact of death necessitates the fact of birth, and students 

 are eagerly seeking the meaning of both. In the lower animals the 

 asexual modes of reproduction seem to provide for the unlimited propa- 

 gation of the species. I say seem, for even in the protozoa conjugation 

 is not proven to be unessential, though an event of comparatively rare 

 occurrence. In animals so highly developed as Arthropoda parthe- 

 nogenesis, pr the development of eggs which have not been fertilized, 

 shows us a way in which higher animals with all their complex organi- 

 zation can be perpetuated by the action of the female sex alone. Upon 

 a zoological philosophy, which should exclude evolution, an explana- 

 tion of sex would be extremely difficult. 



If evolution be the true history of the animal kingdom, and the exist- 

 ing diversity of form be due to transmission from parent to offspring, 

 we can at once see a possible meaning for sex. Evolution requires 

 two factors : the conservative one, by which to explain the resemblances 

 between animals or plants, and another to be the vehicle of divergence. 

 Many facts seem to point to the conclusion that sexuality is the mechan- 

 ism of evolution ; that is, that it is through sexual reproduction that di- 

 vergence in animal and vegetable structure is produced. Thus in 

 horticulture, for instance, it is very noticeably the case that where a de- 

 sirable form is sought to be perpetuated propagation is from buds, 

 grafts, etc., which are asexual products, and not from seeds which are 

 true sexual products. Again, in those cases in the animal kingdom 

 where true parthenogenesis takes place, it is .very strongly held by 

 Brooks, Weismann, and others, though demonstrative evidence has not 



* The Evolution of Sex. By Patrick Geddes and J. A. Thomson. London, 1889. 



