ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
505 
the living body has been taken as granted. And in this given struc- 
ture Driesch includes the conditions of coherence, adaptability, and 
physiological Zweckmassiglceit. What the nature of this “ given living 
Urstruktur” may be is not, of course, at present known, but the hypo- 
thesis of the nucleus being a mixture of ferments is dangled before the 
reader’s eyes. Granted the much-endowed initial order and structure 
— the protoplasmic machine, in short — biology may thereafter become a 
sort of vital mechanics, but only thereafter ; the essential fact of life, 
the structure or “ tektonik,” is only describable, not explicable. The 
assumption is that all the processes of development, function, regenera- 
tion, &o. 9 are implied physico-chemically in the ovum, as the performances 
of a machine in its structure ; but the manner of the implication is beyond 
our investigation. Ail that Driesch ventures to say is that the vital 
force is no specific form of energy. But what is it then ? he asks, and 
leaves us to ask. 
And so the “ machine-theory of life ” ends up, and we feel ourselves 
not much further on. No brief summary can do justice to an essay on 
these intricate questions, but we doubt whether the author’s strong words 
in regard to Darwin and Hegel are justified by his own performance. 
He is not himself quite satisfied, but his answer to the discontented 
is obvious from the delightful note, “ Man wolle aus dieser Selbstkritik 
nicht entnehmen, dass ich einem andereu zugestehe besser fiber 
‘ Entwicklungsmechanik ’ geschrieben zu haben.” An answer from 
lioux * saves Driesch from being wholly left to self-criticism. 
Physiological Interpretations of Striicture/f — Mr. A. T. Masterman 
has an interesting essay “ on some points in the general morphology of 
the Metazoa considered in connection with the physiological processes 
of alimentation and excretion.” He begins by emphasising the fact that 
plants can live on liquid food, while most animals take in solids. Hence 
the continuous envelope of the former, the mouth and alimentary area 
of the latter. Monocytic ingestion occurs primitively as a specialisation 
of locomotor function, and even in Metazoa the same evolution may be 
detected. Thus the ingestive mouth-parts of Arthropods are primarily 
locomotor ; in some Coeientera half of the external surface forms an 
area of polycytic ingestion ; Medusae 4 in. in diameter may have neither 
mouth nor manubrium ; the stomodaeum is another case in point. 
In the monocytic differentiation, the stage after diffuse ingestion 
appears to be the formation of a definite ingestive aperture with stomatic- 
ingestion. In a simple spherical pelagic Metazoan a stimulus to hetero- 
geneity and to a condensation of the area of ingestion is found in the 
dissimilarity in environment between the upper and lower cells. But 
monocytic ingestion in the lowest Metazoa involves the mechanical 
movement of single cells to the interior, and thus we reach hypoblastic 
invagination. Gradually the inwandering of single cells is replaced 
phylogenetically by the immigration of a whole tissue. The same 
arguments may be applied to the evolution of mesoblastic pouches from 
the hypoblast. 
The author proceeds to develope the idea that the perfection of 
polycytic as opposed to monocytic digestion is the key-note upon which 
* Op. cit., pp. 556-8. 
f Zool. Anzeig., xix. (1S96) pp. 190-8, 206-21 (13 figs.). 
2 N 
1896 
