February 11, 1898.] 



SGIENGE. 



199 



trast in color between the tissues of the two 

 species enables one to follow in the living 

 specimen the exact development of each 

 part. If the tail-bud of an embryo (ca. 

 4.5 mm. long) of one species be replaced 

 by a similar portion taken from the other, 

 it may be observed that, as the tail grows, 

 the epidermis from the body moves out 

 over the base of the tail until about the end 

 ■of the sixth day it covers its proximal two- 

 thirds. The underlying tissues (muscle 

 plates, notochord and spinal cord) grow 

 apically, and the place of union between the 

 two portions remains very near to the base 

 of the tail, although it does shift with re- 

 spect to the anus through a distance equal 

 to about three metameres. When several 

 segments of the body are grafted along with 

 the tail, a similar shifting of the epidermis 

 takes place, though less in amount, and even 

 when the two parts are iinited in the region 

 of the pronephros there is a slight backward 

 movement. This is brought about largely, if 

 not entirely, by the pulling of the skin due to 

 the enormous growth of the tail as compared 

 with the body. The parallel between the 

 direction and amount of movement of the 

 epidermis during development,and the mode 

 of distribution of the cutaneous nerves in 

 the body and tail of fall-grown tadpoles, in- 

 dicates that each nerve supplies that region 

 of the integument which, at an early stage, 

 was nearest to it. 



When, in place of a tail-bud which has 

 been removed, a similar portion of another 

 larva is grafted by its distal end, leaving 

 the proximal end free, a tail-like structure 

 is regenerated. In cases where the noto- 

 ■chords of the two parts unite, the regen- 

 erated tail attains a degree of perfection 

 but little inferior to those regenerated from 

 the distal end. If the notochords do not 

 unite, regeneration may take place from both 

 pieces, resulting in a forked tail. When 

 neither the notochords nor spinal cords 

 unite, the tail stump of the stock regener- 



ates, while the grafted piece remains as an 

 insignificant lump on the side of the tail. 



In all cases (six) where virescens tails 

 were grafted to palustris larvse, and in fifty 

 per cent, (four) of the cases in which palus- 

 tris were grafted to virescens larvae, degen- 

 eration of the transplanted tissue took place, 

 beginning sometimes as early as three weeks 

 after operation. This was independent of 

 metamorphosis, having begun before the ap- 

 pearance of the extremities. The tadpoles 

 lived for weeks afterwards with withered 

 tails, without undergoing further metamor- 

 phosis. 



One specimen in which the two parts 

 were united in the region of the pronephros 

 passed successfully through its metamor- 

 phosis. Little or no blending of specific 

 characters could be observed. The head of 

 the frog had the markings of R. virescens, 

 while the body and hind legs had those of 

 R. palustris. 



The Structure and Development of the Excretory 



Organs in Limulus. W. Patten. 



The brick-red gland or coxal gland 

 of Limulus has long been regarded as a 

 ductless gland of uncertain significance, 

 but we are now able to demonstrate that it 

 is provided with a duct several millimeters 

 in diameter and three or four inches long. 



Its development has also been carefully 

 studied, but the structure described as the 

 developing gland proves to be the develop- 

 ing duct ; the embryonic gland was not seen 

 at all. 



Naturally, the conclusions as to the sig- 

 nificance of this organ based on such foun- 

 dations can have but little value. 



The duct in the adult is so thin-walled 

 that it is not readily seen and is very diffi- 

 cult to dissect. But it may be easily injected 

 with either celloidin or asphalt, the mass 

 filling the duct and penetrating all through 

 the lobes of the gland. Isolation is then ef- 

 fected by corrosion with caustic potash. 



