414 D. J. SCOURFIELD OX MENDELISM AND MICROSCOPY. 



aaked eye, appeared to be wholly black, with the exception of 

 the anterior half of the cephalothorax, which was white. 

 Under the microscope the black coloration was seen to be 

 produced by two factors — namely, a beautiful blue and a dark 

 brown — the former being diffused in certain of the tissues, and 

 the latter accumulated in little corpuscles or oil-globules. When 

 preserved in formalin the animals lost their black appearance, 

 and became vividly blue — a colour which they retain at the 

 present time. The change was, of course, due to the disappear- 

 ance of the brown globules. I think there can be no doubt that 

 the two colours in this case would be found to belong to two 

 different allelomorphic pairs, if they could be tested from the 

 point of view of their hereditary behaviour. 



In passing now to a consideration of the third connection 

 between Mendelism and microscopy, which is provided by the 

 possibility of using certain microscopic organisms for experimental 

 work, we are entering upon a more speculative field. So far as 

 I know nothing has yet been done in this direction. There are, 

 however, several reasons why microscopic creatures might be 

 found useful for work on Mendelian lines, provided, of course, 

 that they are bisexual, and not too small to prevent the isolation 

 and control of individuals. Their small size would make it 

 possible to carry on extensive experiments in a small space and 

 in a very inexpensive way. Most of them, also, are very quick 

 and prolific breeders, and many generations could be obtained in 

 the course of a vear. Then, with resrard to the simultaneous 

 study of the germ-cells and body characters, it would probably be 

 found that they would provide much better material than larger 

 animals and plants. Lastly, it would be of the highest theoretical 

 importance to trace the course of heredity of particular characters 

 in cases where parthenogenesis occurs, and such cases can, of 

 course, most easily be found among microscopic animals. 



On the other hand, there are evidently special difficulties 

 connected with the employment of microscopic animals for the 

 purpose indicated. Necessarily they would have to be examined 

 under the microscope, and this would probably involve some 

 increase in the labour of recording the results, and certainly 

 some additional risk of injuring valuable specimens. There is 

 also some uncertainty as to the limits of local and seasonal 

 variation in many cases, and this might make the selection of 



