ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



223 



Visceral Nervous System of Periplaneta orientalis.* — M. 

 Kostler, after a detailed notice of the work of preceding anatomists, 

 commences with the unpaired visceral nervous system, which can be 

 best studied by the method of sections : he finds in it (1) a frontal 

 ganglion ; (2) the nerve on the oesophagus and crop ; (3) the large 

 triangular ganglion on the crop ; and (4) the two nerves thence given 

 off with their accessory ganglia. In the first of these we find the so- 

 called central dotted substance, and it is surrounded by a layer of 

 ganglionic cells ; these last are traversed by a special supporting 

 substance such as Dietl has found in the cerebrum ; from the neuri- 

 lemma surrounding the ganglion fine connective cords pass off in all 

 directions towards the central mass; the ganglionic spheres are 

 always of a larger size than they ever are in the brain; they are 

 rarely pyriform in shape, and never have any investment ; the proto- 

 plasm is collected into nuclear masses of some size, and a concentric 

 disposition of the layers is easily seen. The spheres are almost 

 always unipolar, bipolar cells being very rare, and multipolar only 

 once observed, and this may have been due to an optic illusion. 



The unpaired visceral nerve has exactly the same structure as 

 that of the commissures of the ventral ganglionic chain, and the grey 

 granular fibres call to mind the sympathetics of the Vertebrata. The 

 large ganglion on the crop has a very similar constitution to that of 

 the frontal ganglion. 



With this unpaired system there is correlated a paired visceral 

 system of nerves ; the development of one standing in opposition to that 

 of the other. It consists of a number of small oval ganglia which lie 

 on either side of the median unpaired nerves, and are connected with 

 the brain ; they have the usual fibrillar structure, and have a few 

 elongated ganglionic nuclear masses imbedded in them. Their chief 

 function appears to be to innervate the large salivary glands. 



The true sympathetic nerve can be seen by removing the ventral 

 ganglionic chain, and treating it for a short time with the vapour of 

 osmic acid; two sets of nerves will then be distinguished, for the 

 ventral chain will be found to have taken a distinctly dark coloration, 

 while between the longitudinal commissures much lighter nerves are 

 to be seen. Almost in the middle of every such commissure, alter- 

 nating now to the right, now to the left, there will be seen passing off 

 a fine nerve ; at the level of the ventral ganglia this nerve divides 

 into two parts, each of which swells out into a small spindle-shaped 

 ganglion, and then passes into the lateral nerve given off from the 

 ganglion, its own pale fibres mixing with the cerebro-spinal, and taking 

 the same course as the peripheral nerves. 



The author thinks that when we make a general comparison 

 between the visceral nervous system of Arthropods and of Vertebrates 

 we can have no doubt that the true sympathetic of the one is that 

 also of the other. Its relation to the ventral chain is reversed indeed. 

 The unpaired nerve is cerebral and corresponds to the vagus, and its 

 grade of development is dependent on that of its possessor, so that in 



* Zeitschr. f. Wiss. Zool., xxxix. (1883) pp. 572-95 (1 pi.). 



