312 



SCIENCE. 



[N. S. Vol. I. No. 12. 



at anj^ stage. I understand also that 

 botanists are by no means agreed to accept 

 the Myxomycetes as veritable plants. One 

 cannot bnt ask, Have we not here organ- 

 isms which connect the two kingdoms? 

 Certainly, in using the above definitions in 

 teaching, it will always be easy to specify 

 the one exception oifered by the Mjtco- 

 mycetes and still leave a clear and avail- 

 able conception in the student's mind. 



Other facts, which stand in the way of 

 strictly upholding the two definitions, are 

 encountered among animal parasites. For 

 example, a tape- worm in the intestine does 

 not apparently take up any solid food, but 

 is nourished by absorption through the sur- 

 face of its body of food material in solution. 

 But in these cases we have evidentlj^ second- 

 ary modifications due to the parasitic life, 

 and in the near relatives of the tape- worms, 

 the trematods and planarians, solid food is 

 taken up. It is to be remarked, too, that it 

 is possible, though perhaps not probable, 

 that even tape-worms will be found on more 

 careful study to take up solid food. 



The extent to which it has now been 

 demonstrated that animals take up food in 

 the form of discrete solid particles is not 

 realized generally. The process has been 

 observed with varying degTces of accuracy 

 in the entodermal cells of the digestive 

 tract of hji-droids, ctenophores, planarians, 

 trematods, annelids, Crustacea, insects, am- 

 phibia and mammals, and probably in other 

 forms, which have not come to my notice 

 in this regard. There is here offered a rare 

 opportunity for a valuable research, by 

 making a comparative study of the absorp- 

 tion of solid food. That the protozoa take 

 up particles by means of their pseudopodia 

 is certainly one of the most familiar and 

 most be-taught facts of elementary biology. 



I believe that we can also safely teach 

 that the absorption of solid particles of food 

 is to be considered one of the most essential 

 factors in determining the evolution of the 



animal kingdom. The plant receives its 

 food passivelj' by absorption, and the evolu- 

 tion of the plant world has been dominated 

 hy the tendency to increase the external 

 surfaces — to make leaves and roots. The 

 animal, on the contrary, has to obtain at 

 least the solid part of its food bj^ its own 

 active exertions, and to the effects — through 

 natural selection — of the active sti-uggle to 

 secure food we maj^, I think, safely attribute 

 a large part of the evolution of locomotor 

 nervous and sensory systems of animals. 

 That it has been the onlj' factor cannot be 

 asserted of course for a moment, but it is 

 presumably not going too far in speculative 

 conclusions to look upon it as the most im- 

 portant single factor. An equallj^ impor- 

 tant role must be attributed to the taking of 

 solid food in connection with the evolution 

 of digestive organs, which are ca^dties which 

 hold food material until it is absorbed by 

 the cellular walls of the cavities. Indeed, 

 we may expect to find that the entodermal 

 cavity had originally no digestive function 

 whatsoever, but was merelj' a receptacle to 

 retain the food while the surrounding ento- 

 dermal cells swallowed it at leisui-e. 



With these speculations I will close, ad- 

 ding only that the speculations have in 

 themselves little value, their only value be- 

 ing to suggest lines of research, which ap- 

 pear promising. The sober naturalist avoids 

 the infernal dipsomania for sheer specula- 

 tion, and in this article I have akeady 

 yielded suflBciently to the temptation. 



Charles S. Minot. 



Hakvaed University. 



THE BEST ORDER OF TOPICS IK A TWO- 

 YEARS' COURSE OF ANATOMY IN A 

 MEDICAL SCHOOL^- 



Teachers of anatomy differ so widefy in 

 their views as to the most useful arrange- 

 ment of the various branches of the subject 



*A paper read at the annual meeting of the 

 Association of American Anatomists, in New York, 

 28tli December, 1894. 



