ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 135 



separated groups, thus come to be the most significant organisms in 

 relation to the annual metabolic cycle of our seas and the food supply 

 from our coastal fisheries." The most significant Copepods are — Olthona 

 similis, Pseudocalanus elongafus, Acartia claim, Temora longicornis, 

 Paracalamis parvus and Calanus finmarchicus. Their distribution is 

 not uniform, and variations in the distribution must have a marked 

 effect on the presence and abundance of at least such migratory plankton- 

 eating fish as herring and mackerel. J. A. T. 



Respiration in Fishes, — A. KroctH and Isabella Leitch {Journ. 

 Physiol.,. 11>19, 52, 288-300). Fish blood appears to be subtly adapted 

 to the available supply of oxygen, that of carp, eel and pike, which are 

 occasioually exposed to low oxygen pressure, being different (in dissocia- 

 tion curves) from that of cod, plaice and trout, which normally are 

 never exposed to very low oxygen pressures. The adaptation of the 

 fish blood must be brought about by some substance or substances 

 present along with the htemoglobin within the corpuscles, and the 

 general significance of the haemoglobin being present in semi-permeable 

 corpuscles, and not simply dissolved in the plasma, is ascribed to the 

 fact that the arrangement makes possible the adaptation of the hemo- 

 globin to extremely different respiratory conditions without interfering 

 with the general composition of the blood. A ha3moglobin dissolved in 

 blood plasm can, in- a cold-blooded animal, only be useful at very low 

 oxygen pressure, and that is probably why in Invertebrates the posses- 

 sion of hsemoglobin is restricted to forms which are habitually exposed 

 to such pressures. J. A. T. 



I 



f INVERTEBRATA. 



^%l . Mollusca. 



Muscle-flbres of Molluscs. — R. Anthony {Arch. Zool. Exper. 

 Notes et Revue, 1919, 58, 1-10, 3 figs.). In the adductor muscles of 

 bivalves there are two kinds of fibres : (a) smooth and slowly contracting 

 (the nacreous portion) ; and {h) rapidly contracting and striated, or with 

 lozenge-shaped marking. Those with • the lozenge-shaped marking are 

 intermediate between smooth and striped. In Anomia the same fibre 

 may show both kinds of marking. The transition from smooth muscle 

 to that with lozenge-shaped marking is adaptive to certain functional 

 requirements which the author expounds. J. A. T. 



• y. Gastropoda. 



Dimorphic Spermatozoa in Paludina vivipara. — J. Bront6 

 Oatenby {Quart. Journ. 3Iicr.Sci., 1919, 63, 401-43, 2 pis., 21 figs.). 

 In the case of these dimorphic spermatozoa, the atypic (giant) cells have 

 numerous fine granular mitochondria, while the typic have a very small 

 number of large, stout, rod-shaped mitochondria. In the typic divisions 

 it seemed that in some cases the large rods were merely sorted out into 

 two groups to the daughter-cells, while in other cases the rods were 

 divided in the middle. In the atypic divisions the mitochondria acted 



