STUDIES ON THE NERVOUS SYSTEM OF ORUSTACEA. 495 
necessary to again draw attention to the method of preparation 
adopted for such embryos, when it is desired to obtain staining 
of the longitudinal fibres. The yolk is removed with needles, 
and the embryo placed with the exposed thoracic ganglia upper- 
most in the dilute methylene blue, the abdomen being allowed 
to remain turned in underneath the thorax. The ganglionic 
cord is then cut across, generally at tlie level of the cesophagus, 
and the methylene blue enters the fibres at the wound. In 
preparations so made the elements under consideration (B (4), 
figs. 6 and 7) have frequently taken up the blue, and can be 
well seen on turning the embryo over and lifting back the 
abdomen. The longitudinal fibres of the posterior ganglia 
can be traced through the anterior ones and show no sign of 
terminating. They are clearly continued forward into the 
thorax, although they cannot be individually followed on 
account of the flexure of the abdomen. On turniug the 
embryo back again so that the thoracic ganglia can be ex- 
amined, all the longitudinal fibres coming from the abdomen 
are seen to commence at the wound which has been made, 
and when this wound lies at the level of the cesophagus it is 
obvious that they must be fibres which enter the brain. No 
endings of longitudinal fibres coming from the abdomen have 
ever been observed in the thorax, and preparations of the 
kind just described have been so frequently made that there 
can be practically no doubt that the fibres in question enter 
the brain. 
These elements (B (0), figs. 6 and 7) are evidently the same 
as those seen by Retzius in the abdominal ganglia of the adult 
Astacus. (See ‘ Biol. Untersuch.’? Neue Folge I, pl. xi, fig. 1; 
pl. ix, fig. 4.) 
A pair of elements of this kind, as has been already stated, 
occurs in Abd. vi, and is represented in fig. 7. In this ganglion 
a second pair of elements, whose cells are situated in the 
posterior portion of the ganglion, also frequently stains. The 
fibres from these cells (fig. 7, B (c)) have been traced as far 
forwards as the abdominal flexure, in preparations in which 
the only wound in the thorax has been at the level of the 
