ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
719 
structure, aud are thereby specially distinguished from all the rest. The 
i ntraganglionic continuations of the commissural fibres are chiefly dis- 
tinguished by the fact that most of them are branched. But few traverse 
the internal capsule without giving off numerous branchlets to the dotted 
substance. It is only at two points, and they are in the plane of the 
origin of the nerve-roots, that a branch is given off on either side from 
the bundle of fibrils which passes directly into the root of its side, and 
with it leaves the ganglion. Along the whole of the inner edge of each 
half of the internal capsule there are numerous nerve-branchlets which 
ramify in the dotted substance ; these arise from the axis-cylinders which 
are given off from the roots of the other half of the ganglion. The 
central fibrous mass, or dotted substance of Leydig, is made up of 
elements of various origins; it forms an extraordinarily complicated 
plexus or rather a network of very fine nerve-fibres inclosed in itself ; 
this is partly formed by the branching of the processes of ganglionic cells 
and partly from root-fibres which branch directly, as well as by lateral 
branches of the commissural longitudinal fibres which traverse the 
ganglia. 
Nereis pelagica is an animal well adapted for the investigation of the 
minute structure of the ganglia of the ventral cord by means of methylene- 
blue. Iu all essential points there is a resemblance to what is seen in 
Hirudo. In both the most essential morphological constituents of the 
dotted substance is an extraordinarily complicated plexus of fine and 
very fine nerve-fibres, which have three points of origin. There are 
longitudinal fibres which, on their course through the ganglion, give off 
a number of lateral branches, which branch again. Then there are 
fibres, which, without becoming directly connected with cells, also branch 
considerably in the dotted substance, and, finally, a considerable contin- 
gent is afforded by the numerous secondary branches of the nervous 
processes. In both cases two bundles of fibrils traverse the whole of the 
ganglionic chain; these, in Hirudo , give off a branch at each, but in 
Nereis only to the four thickest roots. 
The results of a few observations on Astacus fluviatilis and Oniscus 
are also given ; in the latter the dendritic branching within the dotted 
substance is richer than has been observed in Worms. 
In conclusion the author examines, in a general way, the results 
he has arrived at, and discusses them chiefly from the physiological 
side. 
Spermatophores as a Means of Hypodermic Impregnation.* — Prof. 
G. 0. Whitman thinks that the following proposition will with difficulty 
be credited : — The spermatophores represent an injecting apparatus, by 
means of which the spermatic elements of one individual are forced 
through the body-wall of another, at any point whatsoever. Such is, 
however, certainly the case, and may be demonstrated as often as one 
pleases, on almost any species of Clepsine . Without affirming it as a 
positive certainty, the author thinks there is evidence, little short of con- 
clusive, that this is the normal method of bringing the sexual products 
together. Long- continued observation under most favourable circum- 
stances has never given him so much as a single indication that the 
* Journal of Morphology, iv. (1891) pp. 361-406 (1 pi.). 
