ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
20 
Excretory System of Animals.* — Prof. L. C. Cosmovici presented to 
tlie second International Congress of Zoology a report on “ What is 
meant by * aquiferous system, segmental organs, excretory organs, 
nephridia.’ ” The following are his conclusions : — 
In every animal organism there is performed the important physio- 
logical process of excretion, which is in most cases effected by glands 
which are more or less simple, more or less metameric, and either reduced 
to a pair of more or less twisted tubes, or consisting of paired renal or 
nephridial glands. We must expel from our scientific nomenclature the 
terms segmental and excretory, for in the first Williams comprehended 
the gonads and their efferent ducts, and by excretion most anatomists 
understand the evacuation of any product whatever. In most aquatic 
animals there is a more or less well organized aquiferous system, which 
is either connected with the circulatory apparatus, when it allows of the 
introduction into the interior of certain quantities of water necessary for 
the erection of locomotor organs (Echinoderms) ; or it is more or less 
in relation with the digestive apparatus (many Protozoa, Sponges, 
Rotifers). In animals which have no nephridia the products of dis- 
assimilation probably fall into the aquiferous system and are thus 
evacuated ; this fact does not authorize us in considering this system 
as homologous with that of the nephridia. We must not confuse the 
efferent ducts of the generative products with the segmental organs, as 
is so often done in Chsetopoda, for the latter appear first and often aid 
the gonads by allowing them to graft on to them their oviduct or 
sperm-ducts. The more or less vesicular tubes of the nephridia always 
terminate by more or less ampullseform extremities which are ciliated 
internally, and they never end by orifices, unless the generative ducts 
are connected with them. 
Studies in Developmental Mechanics.! — Dr. Hs. Driesch has pub- 
lished further investigations and reflections on this subject. Increase of 
temperature separates the two first segmentation cells in Sphser echinus , 
and there result two blastulac loosely connected, or separate from one 
another. The removal of one cell from the 4-cell stage of Echinus does 
not hinder the formation of a normal larva. Indeed, a single quarter 
can develope normally. Warmth may slightly alter the character of the 
segmentation, and yet a normal organism may result. The egg-membrane 
is unessential in segmentation. Segmenting ova abnormally altered by 
pressure may still form typical Plutei. Stages deformed to such an 
extent that they are two-layered plates with eight cells in each layer 
may still turn out normal Plutei — a fact against His’s theory of the 
specific importance of individual blastomeres. What should form one 
pole forms the two sides, and what should form the other pole forms 
both, — which is certainly a notable change. Without inhibiting de- 
velopment, portions may be removed from the segmenting ovum, but 
the portion left must not be less than about a quarter. All these facts 
point to the conclusion that the blastomeres of Echinidse must be very 
homogeneous. Ova which divide simultaneously into four are regarded 
by Fol and by the brothers Hertwig as doubly fertilized. Assuming 
this, Driesch notes that the whole rhythm of division is in these cases 
* Congres Internal, de Zoologie, II. i. (1892) pp. 16-40. 
t Zeitschr. f. Wiss. Zoo!., lv. (1892) pp. 1-62 (3 pie.). See this Journal, 1892, p. 13. 
