ZOOLOGY AND BOTANY, MIOKOSOOPY, ETO. 223 



cussion of the all too-abundant nomenclature, Gilson reports his observa- 

 tions on the development of sperms in certain Myriopods, Insects, Arachnids, 

 and Crustaceans. In doing so the author observes the following order : — 

 (1) The steps in the evolution of the mother-cells, that is to say, the series 

 of cellular multiplications which end in a last generation of sperm cells 

 which are directly transformed into sperms ; (2) the formation of the sper- 

 matozoid, characterized by phenomena of internal differentiation occurring 

 within the protoplasm and the nucleus of the sperm cell ; (3) the special 

 phenomena concerned with the liberation of the ripe sperms. Primordial 

 metrocytes give rise to metrocytes or actual mother-cells (spermatogonia, &c., 

 of authors), and these form spermatic cells (spermatocytes), which develop 

 directly into sperms. Whether the spermatocytes appear as external buds on 

 the metrocyte or by internal endogenous division there, they are. throughout 

 to be regarded as homologous. A more extended notice may be deferred 

 till Gilson's further results on Crustaceans come to hand. 



Nervous System of Insects and Spiders and Remarks on Phxynus.* — 

 Acridium and ThyridojJteryx served Mr. A. T. Bruce for his study of the 

 nervous system in insects. 



The supra-oesophageal ganglion of insects and Arachnids is distinctly 

 double. Each ganglion of the ventral chain is closely invested by mesoblast 

 cells forming a " perineurium," which originates as a median ingrowth 

 along the ventral mid-line. The perineurium also invests the transverse 

 and longitudinal commissures, and each of two adjacent ganglia. These 

 latter are at first solid masses of cells, the central portion of which breaks 

 down and becomes " punktsubstanz " ; by extension laterally and longitudi- 

 nally, this gives rise to the commissures. 



The supra-cBSophageal ganglion has exactly the same structure, and is 

 divided into an anterior and posterior division, separated by perineurium. 

 The "brain" therefore of insects and spiders consists of two pairs of 

 ganglia serially homologous with the ganglia of the ventral chain. The 

 anterior division belongs to the antennal somite, and innervates the 

 antennae of insects and the rostrum of spiders ; both these are special 

 homologues with the first antennae of Crustacea. 



The posterior division belongs to the somite of the upper lip, which is 

 a paired structure in the two insects studied, so that the labrum of insects 

 and spiders is homologous with the second antennae of Crustacea. 



The circum-oesophageal commissures in insects are formed by a back- 

 ward extension of the posterior division of the ganglion, and the nerves 

 coming off from it really belong to the ganglia. 



Some observations were made on the embryos of Phrynus ; the re- 

 semblance of the ventral surface of the adult to that of Limulus is noted. 

 There is a curved process on the inner side of the coxal joint of the last 

 thoracic appendage, corresponding to that of Limulus. Paired structures 

 are present resembling the chilaria. Each of the three last appendages 

 bear episterna. 



On the coxal joint of fourth appendage there is a sense-organ; the 

 epidermic cells are here columnar, and are continued outwards as 

 filaments, several of which enter a single pair, which is the external part of 

 the sense-organ. 



Function of Palps of Myriopods and Spiders.f — M. F. Plateau finds 

 that in the chilopodous Myriopoda, as in mandibulate insects, the palps are 

 not indispensable for capturing prey, recognizing food, or introducing it 



* Johns-Hopkins Univ. Circulars, vi. (1886) p. 47. 

 ■\ Bull. Soc. Zool. France, si. (1886) pp. 512-30. 



