740 SUMMARY OF CURRENT RESEARCHES RELATING TO 



as much reason to recognize volition in the detached parts as in the 

 ciliated Infusoria, from the fact that the direction of the moving pieces 

 of the gill is so frequently changed as they pass from point to point on 

 a moistened plate. In the common sea-mussel there is a latent power of 

 independent movement in the entire animal, as well as in the detached 

 parts, which has hitherto escaped notice. 



Abranchiate Lamellibranchiata.* — Mr. W. H. Dall caUs attention 

 to his work on Cuspidaria and allied forms, which was ignored, he thinks, 

 by M. P. Pelseneer.f Of this M. Pelseneer % offers an explanation, and 

 proceeds to discuss some other points raised by Mr. Dall. The latter 

 had doubted whether the Belgian naturalist had really seen examples of 

 Lyonsiella Sars and Silenia Smith, to which the answer is that the ex- 

 amples of Lyonsiella were named by Mr. Sars, and those of Silenia were 

 the types. There cannot be, as Dall supposes, any progressive develop- 

 ment of the gill from Cuspidaria to Lyonsiella, but the contrary, for the 

 gill is a more archaic organ than the muscular septum. The septa of 

 the Septibranchiata are not, as Dall says, delicate membranes, but thick 

 muscular septa, and the spaces seen are not artifacts, but, as the plates 

 in the ' Challenger ' Eeport show, constant and symmetrical holes, with 

 definite lips. 



Molluscoida. 

 a. Tunicata. 



Origin of Test-cells of Ascidians.§ — Mr. T. H. Morgan has a pre- 

 liminary notice of his investigations on this disputed question. Obser- 

 vations were very satisfactorily made on Cynthia partita. Ova and 

 follicular cells, in their earliest condition, appear as nuclei in the 

 flattened epithelial membrane which forms the wall of the oviduct. One 

 of the nuclei enlarges, protoplasm is formed around it, and it becomes 

 an ovum, around which some of the other nuclei arrange themselves. At 

 the same time the surrounding nuclei collect protoplasm about them- 

 selves, and this spreads over the ovum ; in the layer thus formed the 

 follicular nuclei lie as in a syncytium. These follicular nuclei increase 

 in number by division, and the peripheral zone of proto^)lasm widens; 

 at certain places this zone next projects slightly into the yolk, and at 

 the same time the follicular nuclei migrate into the projections. These 

 plugs of protoplasm, with the contained nuclei, become gradually con- 

 stricted off from the follicular zone and form the test-cells just within 

 the follicle. The ovum, test-cells, and follicular cells are all homologous. 



In Clavellina the young follicular nuclei remain on the outside of the 

 protoplasmic zone ; later, some of the nuclei ruigrate into the zone and 

 the follicular membrane is formed in the centre of this protoplasmic 

 ring; it encircles the^ogg, and test-cells become separated from follicle- 

 cells. 



0. Bryozoa. 



Anatomy of Phoronis australis. |j — Dr. W. B. Benham has had an 

 opportunity of studying the anatomy of this comparatively large species 

 of Phoronis. The mouth is a wide, though compressed, funnel-shaped 

 opening, the corners of which are continued as grooves between the 



* Bull. Soc. Zool. France, xiii. (1888) pp. 207-9. 



t This Journal, 1888, p. 564. J Bull. Soc. Zool. France, xiv. (1889) pp. 111-.3. 



§ Circ. John Hopkins Univ., viii. (1889) p. 63. 



II Quart. Journ. Mi<-r. S.'i., xxx. (1880) pp. 12.^-58 (4 pis.). 



