412 W. H. GASKELL. 



aud the large aorta springing from it are absolutely free from 

 pigment. It is the walls of the large venous spaces, where the 

 blood flow is slow, that are so markedly pigmented. 



Further, in the Ammocoetes, especially near the time of 

 transformation, we find evidence of changes going on in the red 

 blood-corpuscles, remarkably like those which Hunter dis- 

 tinguishes as passive destruction. Here and there, in the 

 neighbourhood of the layers of pigment which have been 

 already formed, especially in the region of the upper branchiae, 

 we see red corpuscles, the nucleus of which does not present 

 the usual finely granular appearance, but, on the contrary, is 

 more or less hidden by large strongly refracting globules of a 

 yellowish-brown tint: in cases where these globules are numerous 

 the blood -corpuscle appears to carry upon its surface an irre- 

 gular-shaped mass of dark brown, almost black pigment, which 

 presents the same appearance as the thinner, more translucent 

 portions of the neighbouring pigment masses. Such appear- 

 ances point strongly to the conclusion that the pigment in the 

 branchiae and other places is due to the accumulation in these 

 places of blood-corpuscles which have undergone passive de- 

 struction similar to the formation of pigment in the spleen. 



This conclusion is rendered certain by the examination of 

 individuals in which metamorphosis has been delayed. In 

 September, 1888, I brought with me from Hind Head, in 

 Surrey, a large number of Ammoccetes of different sizes, vary- 

 ing in length from about 25 to 130 mm. These were placed in a 

 basin containing sand and weed, brought from the stream in 

 which they were living, and the water in the basin was renewed 

 occasionally. A considerable number of these were killed soon 

 after their arrival at Cambridge ; about twenty, however, were 

 left alive, and have continued to live in the sand up to the 

 present time, October, 1889, i.e. more than a year after they 

 were caught. They show no sign of transformation, and have 

 apparently not grown in length, some being still as small as 

 28 mm., others from 40 to 70 mm. I have made series of 

 sections of these Ammoca3tcs through diflPereut regions of the 

 body, the animal having been stained aud prepared for section- 



