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On some Migrations 0/ Cells. 

 By E. Ray Lankester. 



It has been remarked that the lower animals often furnish 

 us with valuable evidence as to the signification of structures 

 and appearances in higher organisms, or man himself, by 

 placing before us those structures in an exaggerated or 

 schematic way, enabling us, as it were by caricature, to catch 

 the true meaning of an arrangement of parts not clearly com- 

 prehensible in the more complex form. Again, a valuable class 

 of evidence is furnished by the study of comparative phy- 

 siology in the kind of natural experiment which certain ani- 

 mals may exhibit in the absence or diminution or increase of 

 organs present in man, the function of which is explained by 

 the habits or condition of life of such animals. Even the in- 

 vertebrata are capable of furnishing evidence of this kind — as, 

 for instance, with regard to hfemoglobin, which is so curiously 

 distributed among Mollusca, Crustacea, and Annelida.^ It is, 

 perhaps, even more largely in the department of histology 

 or minute anatomy that our knowledge of human structure is 

 in intimate relation Avith the study of the lower animals, and, 

 indeed, of plants, for the doctrine of Schwann was based on 

 that of Schleiden. Modern ideas as to protoplasm and the 

 character of cells in the tissues of the highest animals have 

 proceeded from the study of the naked Rhizopoda, and in- 

 creased knowledge of the histology of invertebrata is con- 

 tinually throwing fresh light on that of man himself. 



A most important fact relating to the function of the minute 

 ultimate masses of living matter or cells of the tissues, which 

 has gradually been established during the last year or two, 

 is that certain of them move, not only in the way of sending 

 out processes and retracting them, manifesting contractility, 

 but actually have the power of locomotion, and pass through 

 what appear to be solid, but are rather to be considered as 

 viscid masses Avhich oppose their course, or through yielding 

 points. Thus the out-wandering of the white and red blood- 

 corpuscles through the capillary walls, first observed by Dr. 

 Augustus Waller in 1846, has been established. A still more 

 curious phenomenon is announced by Saviotti, who has ob- 

 served the pigment-cells of the frog's web to pass into the capil- 

 laries, and become carried along in the blood-stream. A third 

 form of locomotion is that noticed by Ecker and Strieker in the 



1 See on this subject, ' Quart. Journ. of Micro, Sci.,' 1869, and ' Journal 

 of Anat. and Pliys.,' Nov. 1869. 



