ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 489 



as magnetite, garnet, and topaz, which by reason of their specific gravity 

 are not to be found in the same sand-strata as the relatively light 

 quartz -grains which are mainly used in the construction of the shell. 

 Some species of Psammosphsera, e.g. P.fusca, build agglutinated shells 

 of sand-grains collected without selection ; P. testacea uses only the 

 shells of dead and living Foraminifera, and it has nothing else to use ; 

 P. parva, finding itself by its small size and free habit liable to suf- 

 focation in the ooze in which it lives, builds a tent-pole arrangement 

 of sponge spicules — several individuals frequently combining to form a 

 mutually supporting mass. This creature fills in the triangular spaces 

 between the main tent-poles with broken spicules of successively gradu- 

 ated lengths, and when it arrives at an awkward terminal space finds 

 and incorporates a truncated triaxial sponge-spicule to fill in the angle. 



Many of the larger Foraminifera are liable to attack from parasitic 

 worms ; thus the softly-agglutinated shells of Grithionina pisum are 

 often bored. But certain individuals of this species protect themselves 

 with a chevaux-de-frise of sponge-spicules, and escape from being bored. 

 In Marsipella cylindrica the investment of sponge-spicules is very friable, 

 the spicules being set parallel to the axis ; in M. spiralis the spicules are 

 twisted into a left-handed spiral, which increases resistance to shock. 

 In Technitella legumm there is an outer layer of sponge-spicules parallel 

 to the axis, and an inner layer at right angles to this. In T. thompsoni 

 "purposive selection" reaches a climax, for out of the vast and hetero- 

 geneous mass of material at its disposal the animal selects only the 

 plates of an Echinoderm, which it binds together at their edges with an 

 invisible cement. 



Bionomics and Reproductive Processes in Foraminifera.* — 

 Edward Heron-Allen contributes an important paper which deals 

 especially with the processes of reproduction and of shell-making. In re- 

 gard to the former, the following conclusions are reached. 1. In certain 

 species of Foraminifera (the number of which will doubtless be increased 

 as investigation continues) reproduction takes place not only by the 

 zoospore method observed by Lister and others, but by viviparity and by 

 the budding-off of young individuals. 2. Viviparous young are formed 

 inside the parent shell, and these young emerge from the parent by the 

 dissolution of the base of the shell. 3. The whole of the protoplasm and 

 internal septa of the parent are used up in this process, whereas in 

 zoospore production the protoplasm only is discharged, the shells of the 

 young being secreted outside the parent, from material derived from the 

 surrounding medium, and not from the internal septa. 4. At certain 

 stages of the life-cycle (as in Arcella) a young individual is budded off 

 from the aperture of the parent and set free at maturity. 5. Under 

 certain circumstances (possibly fortuitous) the protoplasm extruded from 

 two or more shells mingles, as Schaudinn observed, preparatory to the 

 formation of embryonic shells outside the parent, as described by Lister. 

 6. The phenomenon hitherto described as " plastogamy " is in the 

 Foraminifera attributable generally to one or other of these last two 

 processes. 



* Phil. Trans., Series B, ccvi. (1915) pp. 227-79 (6 pis.). 



