ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 409 



olfactory, and the mandibular. The first of these is divisible into two 

 regions, the median optic ganglion which occupies the posterior and 

 superior part of the brain, and the optic lobes which lie laterally and 

 correspond to the optic ganglia of Insects and Crustacea. The former 

 portion is interesting in two points ; in the middle of the cortex of 

 ganglionic cells there are two islets of small nuclei grouped around an 

 eminence of the medullary substance ; these have all the characters of 

 the ganglionic nuclei of Dietl, and may be considered as cells which are 

 very poor in protoplasm. The optic lobes are small cylinders situated 

 at the extremities of the brain ; though their structure is somewhat 

 complicated, it is much simpler than that of the optic ganglia of Insects ; 

 each consists of four layers, internal medullary, layer of optic fibrils, 

 ganglionic layer, and layer of optic bundles. 



The olfactory ganglia are formed by the two olfactory lobes, each of 

 which consists anteriorly of a thick layer of ganglionic nuclei, below 

 which the dotted substance is peculiarly fine and homogeneous. On the 

 outer side the lobe is swollen into a lobule invested by ganglionic cells, 

 in which the dotted substance is differentiated into glomeruli comparable 

 to those of Insects. The mandibular ganglion, which is situated in the 

 inferior and anterior part of the brain, is formed of two lobes united 

 behind by a commissural band, and in front by a well-isolated nervous 

 bridge which gives off" the stomatogastric nerves. Its ganglionic cortex 

 consists only of cells rich in protoplasm. The nervous bridge is formed 

 of a cylinder of dotted substance invested by large cells. There is a 

 transverse commissure of the oesophageal ring, which is formed by a 

 bundle of fibres that take a U-shaped course. 



We may conclude that the brain of lulus is more complicated than 

 that of other Myriopods yet studied by M. Saint-Eemy, and that it 

 presents striking resemblances to that of Insects ; there are traces of the 

 pedunculated body ; the optic ganglion, though complex, has no chiasma ; 

 the olfactory lobe is relatively more important than that of Insects, as 

 in them there are cells poor in protoplasm which are specially reserved 

 for the centres of special sensibility. 



y. Prototracheata. 



Development of the Cape Species of Peripatus.* — Mr. A. Sedgwick 

 continues his account of the development of Peripatus of the Cape from 

 stage G to birth. The changes which take place are mainly those of 

 growth and histological differentiation. The segmented thickenings of 

 the ectoderm which are called the ventral organs are, in the first seg- 

 ment, probably represented by the cerebral grooves ; those of the second 

 differ from all the posterior in not coming into contact with one another 

 in the mid-ventral line ; they remain in the ectoderm and appear to 

 retain a connection with the posterior lobe of the brain ; the ventral 

 organs of the oral papillae become divided into two parts by the lips ; 

 those of the seventeen ambulatory legs appear to retain a cellular con- 

 nection with the lateral nerve-cords. The ventral cords withdraw from 

 the ectoderm, though they still appear to be attached to the latter by 

 marked cellular processes. The changes in the nervous system and eye 

 are described. The crural glands seem to be entirely derived from the 

 ectoderm, but nothing is known as to the details of their development. 



* Quart. Joura. Micr. Sci., xviii. (1888) pp. 373-96 (4 pis.). 



