ZOOLOGY AND BOTANY MICROSCOPY, ETC. 443 



one case three gastrula-rudiments, each with its blastopore. He believes 

 that most double or multiple monstrosities may be attributed to an early 

 mechanical separation of the first blastomeres under the influence of an 

 excess of osmotic pressure. 



Experiments in Grafting Tadpoles' Tails.* — Mr. R. G. Harrison 

 has followed Born in his grafting experiments, and has obtained a num- 

 ber of interesting results. 



The embryos of Bana virescens and Bana palustris are markedly 

 different in colour. The specific coloration, which is due to pigment 

 and yolk granules, is common to all cells. In heteroplastic combina- 

 tions of embryos of these species, made according to Bora's method, it 

 is, therefore, possible to follow in the living specimen, as development 

 proceeds, the movement of any group or layer of cells with respect to 

 the original dividing line between the two constituents. 



The combination of body and head of one species with the embryonic 

 tail-bud of the other, gives the following information concerning the 

 mode of growth of the tail : — (a) The epidermis passes steadily from the 

 body to the tail, shifting over the underlying structures, so that one 

 week after grafting the original epidermis of the tail-bud covers only 

 about one-third (the tip) of the tail. (6) The musculature, spinal cord, 

 and notochord, increase in length, largely by apical growth, and also, to 

 a much less extent, by the pushing of segments (about three) out from 

 the trunk to the base of the tail. 



In the trunk region, the shifting of the epidermis over the under- 

 lying organs becomes less in amount as the head is approached. The 

 movement of the epidermis is due to the tension brought about by the 

 rapid apical growth of the tail, and the absence of a corresponding pro- 

 liferating centre in the epidermis at the tip. The oblique course taken 

 by the cutaneous nerves of the trunk and tail of the full-grown larva and 

 frog, in passing from the vertebral column to their ending in the skin, 

 is due to the ontogenetic shifting of the latter from its original 

 position. 



After amputation of the tail, the peripheral nervous system is regen- 

 erated from the spinal cord. First, a single nerve pair arises from cells 

 lying within the cord. Some of these cells pass out upon the nerve-root 

 and form a large ganglion. Later, a few of the nerve-cells wander 

 further peripherally along the nerve-trunk, forming several (at most 

 three) ganglionic cell-groups. These represent the more distally situ- 

 ated ganglia, lost in amputation, which are never entirely replaced. 



The oral end of an amputated tail-bud has a considerable regenera- 

 tive capacity when the bud is transplanted by its distal end to the body 

 of another individual. The structure then regenerated is tail-like in 

 form, no matter to what part of the body it is attached. When trans- 

 planted so as to replace a normal tail, the resemblance to the latter may 

 become striking. The perfection of the part as a swimming organ is in 

 such cases dependent upon the exactness with which the corresponding 

 tissues of the respective components are united. If the union is imper- 

 fect, forked tails result. The cases in question are not regarded as 



* Bull. Johns Hopkins^Hospital, x. (1899) pp. F.3-94 (2 pis. and 21 figs.). See 

 Arch. Entwickmech., vii. 



