ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
165 
Botryllid bud is wholly ectodermic , excepting some migrant mesoderm 
cells. The fact has been confirmed by several workers, and Hjort now 
investigates the problem in Glossophorum sabidosum. Here the outer 
vesicle of the bud is, as before, continuous witli the ectoderm of the 
parent animal, but this outer layer is passive in the bud-formation ; the 
inner vesicle of the bud is continuous with the epicardium of the parent 
animal and endodermic. Thus in the Botryllus- type, the bud-rudiment 
is practically ectodermic, while in the Polyclinum- type it is endodermic. 
Can we suppose that the rudiment in each case, though topographically 
referable to ecto- or endoderm, is still potentially indifferent and undif- 
ferentiated, or what can we suppose ? 
INVERTEBRATA. 
Physiological Morphology.*— Hr. J. Loeb has described some of his 
interesting experiments in one of the Wood’s Holl Lectures. If apex 
and root-end be cut from an Antennularia , and the stem be hung in water 
in its original position, a new apex with lateral twigs and polyps is 
formed at the upper end, while new roots grow at the lower end. But 
invert the stem, and the original upper end, brought lowest, forms roots. 
When organs grow out of their proper place, Loeb speaks of heteromor- 
phosis. If the stem be fixed horizontally, the downward arms become 
roots, and new stems are developed above (Geotropism). In the polyps 
Margelis and Pennaria, roots grow only when in contact with solid 
bodies, and polyps only when freely washed with -water (Stereomor- 
phism). An excised portion of Cerianthus membranaceus forms tentacles 
only at the oral end (polarization). In diluted sea-water, Tubularia 
mesembryanthemum grows more quickly than in the normal, and vice 
versa ; and great importance is attached to the osmotic factor in growth. 
Sea-urchin ova at the 2-, 4-, or 16-celled stages, were placed in sea- 
water diluted with an equal volume of distilled water ; the ova absorbed 
water, the membrane burst at one place, and part of the protoplasm pro- 
truded in a drop. Beplaced in normal sea-water the eggs formed double 
or triple embryos ; even a non-nucleated protruding drop is said to 
have gained a nucleus and developed into a normal embryo ! 
In the blastula, the cells, whose specific gravity has been decreasing, 
are in contact internally with fluid more dilute than that externally, 
hence a condition of invagination. In diluted sea-water, the tendency 
is rather to evagination. 
Cardiac Activity of Invertebrates.f — Dr. Ph. Knoll has studied 
the heart-beats of various Invertebrates, e. g. Mysis, Porcellana , Squilla , 
Daphnia , Pterotrachea, and Salpa, especially in relation to the influence 
of altered temperature. At temperatures between 15° and 22° C., the 
number of heart-beats per minute differs widely in different forms. 
Thus the beats are uncountable in Copepods, 260 per minute in Mysis , 
23-25 in large Tunicates. In small animals and in small species the 
beats are less frequent than in larger forms. Knoll directs attention to 
the “ explosive ” abruptness of the diastole, especially at temperatures 
* ‘ Biological Lectures delivered at the Marine Biological Laboratory of Wood’s 
Holl, Boston, 1894. Biol. Centralbl., xiv. (1894) pp. 846-8, summary by Prof. J. 
Rosenthal. f SB. K. Akad. Wiss. Wien, cii. (1893) pp. 387-405. 
