ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 203 



Evolution in Sea-pens. — Sydney J. Hickson {Proc. Roy. Soc, 

 1918, 90, 108-35). 1. liadially symmetrical animals, sedentary or 

 drifting in habit, are far more variable in external form and in the 

 number and arrangement of their organs than are bilaterally sym- 

 metrical ani]na]s, free and active in their movements. 2. The 

 radially symmetrical Pennatulids are more variable than the bilaterally 

 symmetrical Pennatulids in almost all the important characters upon 

 which the classification is based. I This is substantiated in detail. 

 3. Particularly in the sedentary animals do we find illustrations of 

 plasticity in specific characters. 4. The more primitive Pennatulids 

 are the radially symmetrical forms, and it is probable that between 

 sedentary Alcyonarian ancestors aud the Pennatulids we know there 

 intervened an intermediate stage with some powers of muscular move- 

 ment, such as a floating or drifting colony. J. A. T. 



Development of Agaricia fragilis.— J. W. Mayor (Froc. Amer. 

 Acad Arts Sci., 1915, 51, 485-511, 6 pis.). An account of the early 

 stages of this coral common on the shore at Bermuda. A pear-shaped 

 planula fixes itself and becomes flattened. The development of the 

 mesenteries, the mesenterial filaments, and the gastro-vascular cavities 

 is described. The gastro-vascular cavity seems to be formed by a 

 breaking down and splitting of the endoderm. The mesenteries, muscle 

 cells and the cells which will form or have formed the mesenterial 

 filaments are the agents which determine its form. An account is also 

 given of the post-larval development, including the earliest stages of 

 the skeleton. The basal plate and the six primary entosepta are the 

 first structures to be developed. The primary exosepta do not arise 

 simultaneously. Bilateral symmetry is frequently shown in the arrange- 

 ment of the primary entosepta. There is considerable varialjility in 

 the development of the septa. J. A. T. 



Ciliation of a Leptomedusan. — James F. Gemmill (Proc. Zool. 

 Soc, 1919, 459-61, 1 fig.). In the gonophore of Melicertidiiim octoco- 

 staturn (Sars) the radial and ring canals are wide enough to allow the 

 action of the ciliated lining to be studied. The ciliary currents are 

 described in the stomach, the manubrial canal, the radial canal, and 

 the ring canal. There is no ciliation on the exi.mbrellar surface, 

 but there is much on the sub-umbrellar surface, and the currents are 

 regular, gathering food-particles to the mouth. The tentacles show^ 

 weak ciliation except on their inner sides near their bases, where they 

 are ciliated more strongly. Their ends are sometimes turned into the 

 mouth. The ciliation of the gastrovascular lining subserves in the first 

 place the mixing and transport of the food, and is also capable of aiding 

 the ingestion of small food particles and the evacuation of the sex-cells 

 through the mouth. J. A. T. 



Somatic and Germ-cells in CoBlentera. — George T. Hargitt 

 (Proc. Amer. Soc. Zool. in Anat. Record, 1920, 17, 327). All cells of 

 the Hydrozoan body, except perhaps the stinging-cells and the nerve- 

 cells, are capable of further differentiation in various directions. This 

 includes the power of de- differentiation and of specialization in a new 



