ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 19 



sharp boundary between nucleus and cell-body disappears, until the 

 formation of a new membrane round the daughter-figures. 



(2) During the mitosis the connection between cell-body and nucleus 

 is much more intimate than obtains with tho resting nucleus. This is 

 probably due to the mixture of " nuclear sap " and the " interfilar mass." 



y. General* 



Aquatic Locomotion.f — M. Amans has made a mechanical study of 

 the modes of aquatic locomotion effected by solid jointed levers. All 

 animals with such apparatus are bilaterally symmetrical ovoids. The 

 mechanical relations of various ovoids are described. He draws a 

 parallel between forms of ovoid and fin, distinguishing on the one 

 hand (a) spheres (lower organisms), (b) circular ovoids (ciliated 

 echinoderm larvae), (c)' elliptical ovoids (vermiform organisms), (<P) 

 unisymmetrical ovoids (most Vertebrates and Arthropods), and (e) 

 asymmetrical ovoids (Pleuronectids, certain Crustacean and Arthropod 

 larvae). As parallel to these he notes the following forms of fin: — 

 (a) embryonic bud, (b) circular cone (vibratile cilia), (c) bisymmetrical 

 cone, the basilar section of which forms an elongated ellipse (ap- 

 proached by dorsal fin of Hippocampus), (cl) unisymmetrical cone 

 (dorsal, anal, caudal fins), and (e) asymmetrical cone (pectorals and 

 abdominals), the base of which forms an oval analogous to the contour 

 of the profile. He distinguishes the various forms of torsion in the 

 appendages, and emphasizes the enormous influence of the resistance of 

 the water on the form both of the body and of its appendages. 



B. INVERTEBRATA. 



Mollusca. 



£. Gastropoda. 



Larval Anal Eye in Opisthobranch Gastropods4 — Prof. H. de 

 Lacaze-Duthiers and M. G. Pruvot report the presence of a remarkable 

 sensory organ in all the embryos of Opisthobranch s which they have 

 examined — Aplysia, Bulla, Pleurobranchus, Boris, and others. It is an 

 eye of a size relatively colossal, for it is one-fifth of the total height of 

 the embryo. It has been particularly studied in Pliiline aperta, where a 

 small lobe, destined to form the intestine, is detached on the right side 

 of the endodermal sac, at about the fiftieth hour. At the same time, and 

 just above it, four ectodermal cells, belonging to the ventral surface of 

 the embryo, become slightly raised and begin to be charged with fine 

 pigment-granulations of the brightest carmine colour. They are so 

 arranged as to form a cross with the angle turned upwards ; in this 

 cavity a fifth ectodermal cell appears, which will give rise to the crys- 

 talline element ; it gradually becomes a rich yellow colour, but does not 

 lose its transparency; it is spherical, with a diameter of 15 /x. The 

 four peripheral cells soon encircle it in such a way as to leave at the 

 tip a small pupil, which is elongated transversely. Just by the upper 

 extremity of the eye a small tuft of vibratile cilia make their appear- 

 ance, and indicate the proximity of the future anus. 



Just before the larva escapes, that is, about the sixth day, the anal 



* This section is limited to papers which, while relating to Vertebrata, have a 

 direct or indirect bearing on Inveitebrata also. 



t Comptes Rendus, cv. (1887) pp. 103.5-7. J Ibid., pp. 707-10. 



C "2 



