ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
70 L 
plasma. They seem to take no direct part in the production of nucleated 
red corpuscles or erythroblasts ; after a certain period the nucleus alters 
in such a way that it stains diffusely and then fragments. This seems to 
be a degenerative change, and probably ends in the total disintegration 
and total dissolution of the cell. 
7 . General. 
Production of Light by Animals and Plants.* — M. E. Dubois has 
been led by a long series of investigations to the conclusion that the 
production of light in both animals and plants is connected with the 
conversion of colloidal protoplasmic granules into crystalloidal granules 
under the influence of respiration. 
Origin of Vertebrates from a Crustacean-like Ancestor. f — Dr. W. 
H. Gaskell proposes to discuss, in a series of chapters, the origin of 
Vertebrates from a Crustacean-like, or more properly proto-Crustacean, 
ancestor. He commences by marshalling the evidence given by the 
central nervous system and pineal eyes of the Ammocoetes of Petromyzon 
planeri. The central nervous system of all Vertebrates consists of two 
parts — one nervous and one non-nervous ; the latter is in part free from 
admixture with nervous elements, and partly helps to form the supporting 
tissue for them. This non-nervous part forms a canal round which the 
nervous material is grouped in the same manner as the nervous system 
is grouped around the alimentary canal. This similarity of grouping is 
not merely anatomical, but is also physiological ; the functions of the 
supra-oesophageal ganglia, of the infra-oesophageal, and of the ventral 
chain, correspond to the functions of those parts of the Vertebrate central 
nervous system which are situated in the same anatomical position, with 
respect to the non-nervous tube, as the corresponding ganglia of the 
Crustacean with respect to the alimentary canal. From these facts Dr. 
Gaskell has already drawn the conclusion that the non-nervous tube of 
the Vertebrate central nervous system is the altered alimentary canal of 
the Crustacean ancestor of Vertebrates. 
What, therefore, we may expect to find in a very low Vertebrate are 
more conspicuous vestiges of the mouth, oesophagus, and cephalic 
stomach than in higher forms ; the pineal eye should be easily recog- 
nizable, and of a Crustacean type, while the proportion of nervous to 
non-nervous material should approach nearer to that found in Crus- 
taceans than in higher Vertebrates. Similarly there should be in 
Ammocoetes something comparable to the large glandular organ known 
as the liver in Crustaceans. 
In searching for the cephalic stomach, or for the mouth and 
oesophagus, Dr. Gaskell thinks his requirements are fulfilled, and 
further evidence in support is afforded by the relation of the infra- 
oesophageal and thoracic ganglia to the walls of the cephalic stomach, 
and the relation of the ventral ganglia to the walls of the intestine. 
The peculiar tissue, which is different from any other, the cells of which 
appear degenerated, which contains lines of pigment between its cells, 
which is found only in lower Vertebrates, and is gradually pushed out 
of existence in the higher classes as the brain increases in size, fills up 
* Comptes Rendus, cxi. (1890) pp. 363-6. 
t Quart. Journ. Micr. Sci., xxxi. (1890) pp. 379-444 (4 pis.). 
3 D 
1890. 
