ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 791 



connected with the nervous system. The author makes additions to 

 our knowledge of the metamorphoses of the cephalic end of the 

 body. 



In describing the development of the organs, the ectodermal 

 structures are first dealt with ; the nervous system, the ventral 

 organs, and the slime-glands are especially noticed. The eye is 

 developed very simply and has only a secondary connection with the 

 brain. Of the mesodermal structures the first to be described are 

 the segmental cavities ; the primitive cavity becomes divided into 

 three parts, which communicate with one another, and one of them 

 becomes the infundibulum of the segmental organ. The paired 

 segmental organ of the segment which carries the slime-papillse 

 undergoes the most remarkable changes, for it becomes converted into 

 the salivary gland. This change occurs only at a late period. The 

 existence of its segmental funnel seems to have escaped the notice of 

 earlier observers. The generative organs appear to be nothing else 

 than modified segmental organs ; the author gives a very detailed 

 description of their development, and points out that the ovary is the 

 homologue of the testis, the receptaculum seminis and receptaculum 

 ovorum of the vas efferens, the uterus of the seminal vesicle and vas 

 deferens, and the vagina of the spermatophoral region and the ductus 

 ejaculatorius. 



The author concludes with some remarks and criticisms of the 

 work of other naturalists who have studied Peri^jalus. 



8. Arachnida. 



Brain of the Scorpion.* — M. G. Saint-Remy finds that the brain 

 of the scorpion is formed by a central mass of medullary substance, 

 which above, in front, and partly at the sides, is invested by cellular 

 layers. Towards the mid-third of its height the medullary substance 

 forms the greater part of the mass ; superiorly the medullary sub- 

 stance occupies only a part of the anterior surfaces, and tho distinc- 

 tion into two halves is better marked. More than two-thirds of the 

 supra-cesophageal mass represents the optic ganglion, and from it arc 

 given off two pairs of optic nerves. In the lower third of the brain 

 the median groove grows shallower and shallower. At the plauc of 

 passage of the oesophagus the lateral cellular investment is, on its 

 externo-latcral surface, continuous with the corresponding commis- 

 sure. Eecent researches have shown that in spiders this portion 

 represents the original ganglia of the chelicera3 ; in the adult 

 scorpion the common ganglion of the cheliceraa commences a little 

 below the passage of the oesophagus. It gives rise to the two paired 

 nerves of the chclicene, and to an unpaired median nerve. The 

 nerve-centres arc enveloped in an external neurilemma provided with 

 flattened nuclei, and in an internal neurilemma ; fine fibres unite 

 these two and form branches in the intermediate space. 



* Comptes Rendu?, oii. (18S6) pp. 1492-4. 



