tHE DEVELOPMENT OF ADMETUS PUMILIO. 619 



nowhere been able to obsei'vo a branching of the tubes, I 

 suppose that it must be simple in its whole length, as in other 

 Arachnids. 



The cavity of the gland is about "01 mm. wide. The cells 

 composing the tube have very distinct cell-walls, the cell- 

 plasm being very clear and staining very slightly. The 

 nuclei are perfectly round, and do not stain very deeply ; 

 their diameter is "007 mm. They lie almost always on the 

 side of the cells nearest to the lumen of the gland, leaving, 

 however, a space between themselves and the cell-walls. In 

 this space the plasm seems at its thickest. The length of 

 the cells, measured from outside the gland to the cavity of 

 the gland, is "02 mm. 



The tube forming the gland itself is enclosed in a sheath 

 of flat cells, of mesodermatic origin, as in other Arachnids. 

 The space between the windings of the tube is filled out by 

 connective tissue. The whole gland is likewise covered by 

 an outer skin, the elements of which somewhat resemble 

 those forming the sheath of the tabule. 



5. TheCentr^al Nervous System. — The nervous system 

 now consists of the cerebral ganglion, the ventral gan- 

 glion-cord, and the nerves. 



When compared with the fourth stage, the ventral gan- 

 glion-cord appears much contracted. In the fourth stage it 

 was continued far into the abdomen, now we only meet with it 

 in the cephalothorax. 



A great advance on the fourth stage is also to be observed 

 m the development of the ganglia. In Stage IV it was im- 

 possible to distinguish them from each other; now they are 

 very distinct. The whole brain has become very similar to 

 that of the adult. 



The outer form is to be seen in the illustration (fig. 2), 

 made after a model constructed by me from a section-series. 

 I will begin by a description of the superficial appearance of 

 the brain. 



A glance at the illustration will show that the brain con- 

 sists of two parts, a smaller doisal and a largei- ventral. It 



