THE EVIDENCE OF THE THYROID GLAND 211 



is there because it is the remnant of the great glandular mass which 

 so closely surrounds the brain and alimentary canal in animals such 

 as Limulus. In my paper in the Quarterly Journal of Microscopical 

 Science, in which I was comparing the tube of the vertebrate nervous 

 system with the alimentary canal of the invertebrate, I spoke of this 

 tissue as being the remnant of the invertebrate liver. At the same 

 time the whole point of my argument was that the glandular material 

 surrounding the brain of Limulus was made up of two glands — liver 

 and generative gland — so that this tissue might be the remnant of 

 either one or the other, or both. All I desired, at that time, was 

 to point out the glandular appearance of this so-called packing tissue, 

 which surrounded the brain-region of Ammoccetes, in connection with 

 the fact that the brain and alimentary canal of Limulus were closely 

 surrounded with a glandular mass composed partly of liver, partly of 

 the generative gland. At present, I think these large cells found 

 round the brain in Ammoccetes are much more likely to be the 

 remnant of the generative gland than of the liver ; the size of the 

 cells and their arrangement recalls Owen's picture of the generative 

 gland in Limulus, and seeing how important all generative glands 

 are in their capacity of internal secreting glands, apart entirely from 

 the extrusion of the ripe generative products, and how unimportant 

 is an hepato-pancreas when the alimentary canal is closed, it is much 

 more likely that of the two glands the former would persist longer 

 than the latter. It may be that all that is left of the old hepato- 

 pancreas consists of the pigment so markedly found in between these 

 cells, especially at the place where the old liver-duct reaches the 

 surface of the brain ; just as the only remnant of the two pineal eyes 

 in the higher vertebrates is the remains of the pigment, known as 

 brain-sand, which still exists in the pineal gland of even the highest 

 vertebrate. This, however, is a mere speculation of no importance. 

 What is important is the recognition of this tissue round the brain 

 as the remnant of the glandular mass round the brain of animals such 

 as Limulus. Still further confirmation of the truth of this comparison 

 will be given when the origin of the auditory organ comes up for 

 discussion. 



I conclude, therefore, from the evidence of Ammoccetes, that the 

 generative glands in the ancestral form were situated largely in the 

 cephalic region, and suggest that the course and direction of the ciliated 

 pseudo-branchial grooves on each side indicate the direction of the 



