ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
345 
Some notes are next given on the nervous system and sensory organs, 
the enteric canal and glands, the circulatory and respiratory organs, and 
those of reproduction. 
The fact that the copulatory apparatus is formed from two rudi- 
mentary appendages of the left side shows that the Pliyllopod-like stem- 
forms of the Ostracoda had a larger number of limbs, and that the number 
— seven — found in Ostracods is a reduction. It remains doubtful whether 
the same appendages have been retained in the various families. 
Nervous System of Diaptomus.*— M. J. Richard has studied the 
nervous system of several species of this genus of Copepods, and finds 
them to agree in the characters now to be mentioned. The system is 
composed of a large supra-oesophageal ganglion united by two con- 
nectives with a suboesophageal ganglionic mass which is continuous with 
a ventral chain which is prolonged as far as the point of insertion of the 
fourth pair of limbs. The brain is an irregular mass formed of a central 
nucleus of dotted substance invested in a layer of cellular elements ; this 
layer varies in thickness at different points. A primary may be distin- 
guished from a secondary brain ; the former consists largely of dotted 
substance, the latter is almost exclusively formed of nerve-cells. The 
nerves given off from the brain are those for the frontal organ, three for 
the eyes, two for the first pair of antenna3, and an azygos ventral branch 
which passes to the labrum. 
The connectives of the oesophageal collar are very strong at their 
point of origin, and have nerve-cells scattered more or less over the 
whole of their outer side, but none on the inner ; nerves are given off to 
the second pair of antennse; a little lower a large nerve passes into 
the labrum ; below, the two connectives are united by a transverse 
commissure. 
The suboesophageal mass is formed of several ganglia and has the 
form of a band, wide anteriorly, which diminishes slightly in width at 
the level of the first maxillipede. There are three cellular swellings 
whence nerves are given off to the mandibles, maxilhe, and maxillipedes. 
Between the first and second thoracic ganglia the ventral chain is 
reduced to a feeble cord, oval in section anteriorly and almost circular 
further back. These thoracic ganglia do not agree in the relations 
which they bear to the corresponding appendages. At the level of the 
fourth pair of limbs the ventral chain bifurcates at a ganglionic centre, 
whence nerve-trunks are prolonged into the abdomen, and which cor- 
responds to a fifth ganglion. A rather large number of nerves is given 
off from the course of this ventral ganglionic chain. 
Various parts of the nervous system exhibit regular lacunae, which 
are continued through a long series of sections an l are seen to form 
true canals which are, no doubt, destined to serve for the nutrition of 
the nerve-chain. The parts are enveloped in an extremely delicate 
neurilemma which is, at points, difficult to see. The author adds that 
he has never come across the “classical” nerve-cell with its abundant 
protoplasm ; all the cells were of the ordinary unipolar type. 
A condition of things very similar to that of Diaptomus is to be 
found in Heterocope saliens. 
* Bull. Soc. Zool. France, xv. (1891) pp. 212-8. 
