940 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tho proliferating cells retains its great size throughout life, and this 

 finally takes up its position on one side of the medulla belonging to the 

 eye from which it arose. 



The author thinks that the history of these cells afifords excellent 

 evidence in proof of the theory which explains the presence of inter- 

 cellular nerve-fibres, by supposing them to be the outer ends of sensory 

 cells, now converted into ganglionic cells. 



The optic ganglion of the convex eye of Arthropods is composed of 

 three lobes ; the first always, and the third sometimes, disappear ; the 

 second gives riso to the optic ganglion proper. The retinal ganglion is 

 a secondary product, and is not formed by invagination. The three-lobed 

 optic ganglion of tlie convex eye of Arthropods is derived from a three- 

 segmented larval ganglion, every segment of which belongs to a pair of 

 larval ocelli. The first, second, and third segments of the optic ganglion 

 of Acilius-larvifi are respectively homologous with the second, first, and 

 third lobes of the optic ganglion of the comjiound eye, and so it follows 

 that the optic ganglion proper of the compound eye is derived from tho 

 first segment of the larval ganglion, or that one which is united with tho 

 large, posterior, dorsal ocellus. The optic ganglion contains six medulla), 

 every one of which corresponds in structure to that of the ganglion to 

 which it belongs, and this indicates that the arrangement of the medullary 

 fibrillfB is as nearly like that of the retinidial fibrillae as existing con- 

 ditions will allow. 



The structure of the retina in the larval ocelli of Insects is much like 

 that of Myriopods, and the whole eye is composed on the same plan as 

 that of Peripatus and of most Molluscs. Mr. Patten believes that the 

 primitive ganglion-cells were tripolar, and were derived from tripolar 

 neuro-cpithelial cells. The outer extremities of these cells were re- 

 duced to intercellular nerve-ends, the bases of which, in Acilius, became 

 tho protoplasmic prolongations of the ganglion-cells, and are, probably, 

 homologous with the axis-cylinders of Vertebrates. 



Spermatogenesis of Arthropods.* — Prof. G. Gilson concludes his 

 series of comi)arativc researches on the spermatogenesis of Arthropods. 

 The first part of his memoir contains an account of the spermatogenesis 

 of Gamasidfe and Ixodidse. (1) The mother sperm-cells multijily solely 

 by binary segmentation. (2) Each resulting sperm-cell contains a large 

 nucleus, rich in karyoplasma, lodging a nucleolus. The cell elongates, 

 the nucleus likewise, the nucleolus retains its form. (3) The adult 

 spermatozoa are free and immobile, but exhibit movements in the female. 



The gi-eater part of Gilson's memoir is devoted to a synthetic survey 

 of his previous results. Throughout Arthropods, he discusses the struc- 

 ture of the spermatozoa as regards form, nucleus, and protoplasm, and 

 then notes the condition of the adult sperms when free or contained in 

 the manifold spennatophores. His general conclusions are disappointing. 

 He first notices the generalizations of Kolliker, Schweigger-Seidel, and 

 de la Valette St. George, but does not admit that they are general or 

 complete. Nor is he satisfied with the theory proposed by Sabatier, nor 

 with the homologies pointed out by P. Geddes and J. A. Thomson. 

 Gilson himself distinguishes three stages of cell-multiplication and 

 differentiation, but maintains the impossibility of formulating any law of 

 spermatogenesis. 



• La Cellule, iv. (1888) pp. S5I-446 (1 pi.). 



