ADDRESS. 9 



intimacy of their union, are far from losing their individuality. Examine- 

 under the microscope a drop of blood freshly taken from the human 

 subject, or from any of the higher animals. It is seen to be composed of 

 a multitude of red corpuscles, swimming in a nearly colourless liquid, and 

 along with these, but in much smaller numbers, somewhat larger colour- 

 less corpuscles. The red corpuscles are modified cells, while the colour- 

 less corpuscles are cells still retaining their typical form and properties. 

 These last are little masses of protoplasm, each enveloping a central 

 nucleus. Watch them. They will be seen to change their shape ; they 

 will project and withdraw pseudopodia, and creep about like an Amoeba. 

 But, more than this, like an Amoeba, they will take in solid matter as 

 nutriment. They may be fed with coloured food, which will then be 

 seen to have accumulated in the interior of their soft transparent proto- 

 plasm ; and in some cases the colourless blood-corpuscles have actually 

 been seen to devour their more diminutive companions, the red ones. 



Again, there are certain cells filled with peculiar coloured matters, and 

 called pigment-cells, which are especially abundant, as constituents of 

 the skin in fishes, frogs, and other low vertebrate, as well as many inver- 

 tebrate animals. Under certain stimuli, such as that of light, or of 

 emotion, these pigment cells change their form, protrude or retract 

 pseudopodial prolongations of their protoplasm, and assume the form of 

 stars or of irregularly lobed figures, or again draw themselves together 

 into little globular masses. To this change of form in the pigment-cell 

 the rapid change of colour so frequently noticed in the animals provided 

 with them is to be attributed. 



The animal egg, which in its young state forms an element in the 

 structure of the parent organism, possesses in the relations now under 

 consideration a peculiar interest. The egg is a true cell, consisting essen- 

 tially of a lump of protoplasm enclosing a nucleus, and having a nucleolus 

 included in the interior of the nucleus. While still very young it has no 

 constant form, and is perpetually changing its shape. Indeed, it is often 

 impossible to distinguish it from an Amoeba ; and it may, like an Amoeba, 

 wander from place to place by the aid of its pseudopodial projections. 

 I have shown elsewhere 4 that the primitive egg of the remarkable hy- 

 droid Myriothela manifests amoeboid motions ; while Haeckel has shown 5 

 that in the sponges certain amoeba-like organisms, which are seen 

 wandering about in the various canals and cavities of their bodies, and 

 had been until lately regarded as parasites which had gained access from 

 without, are really the eggs of the sponge ; and a similar amoeboid con- 

 dition is presented by the very young eggs of even the highest animals. 



Again, Reichenbach has proved 6 that during the development of the 



* On the Structure and Development of Myriothela. Phil. Trans, vol. 165, 1875, 

 p. 552. 



s Jenaische Zeitschr. 1871. 



6 Die Embryonanloge und erste Entwickelung des Flusskrebse. Zeitschr./. wistent. 

 Zoologie, 1877. 



