ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 521 



the foot ; the endeavour to attain this stable position was the reason for 

 the forward displacement of the branchial cavity from its originally 

 posterior position ; the gonad supplied the impulse to the formation of 

 the spiral shell, which was primitively so disposed that its free margin 

 with the notch was turned backwards ; the degeneration of the right 

 gonad, associated with a protrusion of the visceral sac, led to a series 

 of displacements ; the apex of the visceral sac first inclined to the left, 

 and then became coiled in a spiral ; the visceral sac and the shell cover- 

 ing it thus disturbed the balance, and there came about a twisting of the 

 shell-apex posteriorly and to the right. 



Centrosome and Sphere in Crepidula.* — Prof. E. G. Conklin summa- 

 rises that part of his work on the maturation, fertilisation, and cleavage 

 of Crepidula, which bears upon the questions connected with the centro- 

 some and centrosphere. He finds that there is a remarkable parallelism 

 between nucleus and centrosome; both arise from granules derived from 

 a mother structure, the chromosomes in one case and the central 

 corpuscle in the other ; in each case only a small fraction of the mother 

 structure gees to form the daughter-structure. Both grow rapidly, 

 absorbing achromatic substance from the cell-body, and then, by the 

 dissolving of their outer membranes, the contents are set free in the 

 cell-body, only the granules mentioned above persisting. The centro- 

 spheres are composed of a specific substance temporarily differentiated 

 from the other cell-contents, which is not self-propagating, but arises 

 anew in each cell generation. This substance forms a large part of the 

 spindle and aster, and at the close of karyokinesis is collected into a 

 large sphere surrounding the centrosome, which ultimately disintegrates 

 into coarse granules. This sphere is apparently the homologue of 

 Meves' idiozome. 



Genus Harpa.f — Dr. R. Bergh describes the structure of Harpa, 

 which has been rarely investigated. The animal has a very large some- 

 what flattened foot, which cannot be withdrawn into the shell, and is 

 without an operculum. There is an anterior lateral notch, which divides 

 the foot into an anterior crescentic broader portion, and a much longer 

 pointed posterior portion. The hindmost part can be thrown off in 

 autotomy. The respiratory tube is long. The long closely adjacent 

 tentacles bear above their middle, externally, a strong optic prominence. 

 In the structure of the nervous system there is a close resemblance to 

 the Buccinidse, but the ganglia are still more concentrated. There is a 

 very narrow mouth-opening, a very long proboscis, a very small gullet, 

 and a radula with three rows of teeth. The salivary glands are very 

 strongly developed, but the intestine is not long, nor the " liver " large. 

 The seminal duct is either an open groove along the posterior border of 

 the very strong somewhat compressed unarmed penis, or it runs sub- 

 cutaueously on and through this organ. The Harpidge are probably 

 close to the Olividee. Bergh describes H. ventricosa, H. rosacea, H. 

 nablium, and H. minor. 



Structure of Neuroglia in Snail. J — H. Smidt corrects some errors 

 in his previous descriptions of this substance. He now finds that the 



* Anat. Anzeig., xix. (1901) pp. 280-7 (8 figs.), 

 t Zool. Jahrb., xiv. (1901) pp. 609-29 (1 pi.). 

 X Anat. Anzeig., xix. (1901) pp. 267-71 (5 figs.). 



