TRANSACTIONS OF SECTION I. 967 
Internal to the epithelial cells of the skin of Ammoccetes is a remarkable 
layer of tissue, generally called connective tissue. It resembles, however, histo- 
logically, in the Ammoccetes, a section through chitin most closely ; the layers 
are perfectly regular and parallel; cells are found in it with great sparseness, and 
it is not until after transformation, when it is altered and invaded by new cell 
elements, that it can be looked upon as at all resembling connective tissue. It 
resembles chitin in its reaction to hypochlorite of soda. In order to completely 
dissect off this laminated layer from an Ammoceetes, all that is necessary is to 
place the animal in a weak solution of hypochlorite of soda, and in a short time it 
entirely disappears, bringing to view the muscles, branchial cartilages, pigment, 
front dorsal part of the central nervous system, &c., in a most striking manner. 
At present I am puzzled that so manifest a chitinous covering should lie internal 
to the epithelial cells of the surface; such a position is not, however, unknown 
among invertebrates, and may be accounted for in various ways. 
For the sake of clearness I will sum up before you in the form of a table the 
corresponding parts in Ammoccetes and in Limulus and its allies, as far as I have 
discussed them up to the present, from which you will see that there is not a 
single organ which is present in the prosomatic and mesosomatic regions of 
Limulus and its allies which is not found in the corresponding situation and of 
corresponding structure in Ammoccetes. 
Table of Coincidences between Limulus and its Allies, and between 
Ammocetes and Vertebrates. 
LIMULUS AND ITS ALLIES. AMMOC@TES AND VERTEBRATES. 
Central Nervous System. 
Supra-cesophageal ganglia. . Cevebral hemispheres. 
Optic part. ; H . Optic thalami, ganglia habenule, &c. 
Olfactory part é : . Olfactory l»bes. 
(Esophageal commissures . - Crura cerebri. 
Infra-cesophageal ganglia. . Epichordal brain. 
Prosomatic ganglia P - Hind brain, cerebellum, post-corp. quadrig. 
Mesosomatic ganglia, - Medulla oblongata. 
Ventral chain. 
Metasomatic ganglia. - Spinal cord. 
Alimentary Canal. 
Cephalic stomach , ° ° . Ventricular cavities of brain. 
Straight intestine e : - Central canal of spinal cord. 
Terminal part 2 : . Neurenteric canal. 
Qsophagus . : 5 : . Infundibular tube and saccus vasculosus. 
Mouth tube . F : ‘ . Hypophysial tube, later nasal canal. 
Liver . . Part of subarachnoideal glandular tissue. 
Appendages and Appendage Nerves. 
Prosomatic or locomotor append- 
ages . Pp : “ . Appendages of oral chamber or stoma- 
todzum. 
Foremost appendages . - Upper lip and tentacles. 
Last appendages , - - Velar appendage and median ventral 
tentacle. 
Metastoma . : : - Lower lip. 
Nerves of prosomatic appendages. Various branches of Vth nerve. 
Mesosomatic or branchial append- 
ages . A - : . Appendages of branchial chamber. 
Opercular appendages . . Appendage innervated by VIIth nerve. 
Genital part . : . ‘Thyroid glandand pseudo-branchial groove. 
Branch. part . i - Hyobranchial. 
Basal part - : . Septum of stomatodzum. 
Branchial appendages Branchial appendages innervated by IXth 
and Xth nerves. 
Speciai Sense Organs and Nerves. 
Lateral eyes and optic nerves . Lateral eyes and optic nerves. 
Median eyes and nerves j . Pineal eyes and nerves. 
