PACKARD. | TRANSFORMATION OF ARTEMIA. 485 
of the influence of the organism upon the surrounding element. The 
hightening of the density of the salt water is naturally accompanied by 
a decrease of aeration in such a water, but this decrease again must 
produce in Artemia an enlargement of the breathing surface, i. ¢., the 
surtace of the gill-sacs. Concerning the posterior branchial lobes, they 
(partly also the gill-sacs) have to enlarge themselves in water of high 
density as auxilliary organs of locomotion, perhaps they also serve as 
auxilliary organs in respiration, especially in Artemia, wherein the pos- 
terior branchial lobes are marked out for their greater tenderness, than 
generally in Branchipus, in which they often are margined with tooth- 
like spines or lttle-developed bristles, being, as it were, the beginning 
ot bristles and spines developed on the other branchipeds. 
According to Leydig’s view the gill-sacs of Artemia and Branchipus 
do not serve as special respiration organs; but the investigation of 
Claus! and Spangenberg? make it in the highest degree probable that 
the inference that the gill-sacs, but not the posterior branchial lobes, 
are not special respiration organs, is a proper one. Such a conclusion 
will also be made by the consideration of these appendages in their re- 
lation to the surrounding element, under which latter I not only mean 
the density of the salt water, but also the temperature; toward the latter 
the gill-sacs are especially sensitive in a high degree, as we shall see 
further on. 
From such a great sensibility of these appendages toward the sur- 
rounding element, we must assume that they have a considerable size 
in specimens with the characters of Artemia milhausenii, not only owing 
to retained growth of A. salina, whose younger specimens have larger 
appendages, but also in consequence of their accession, owing to aug- 
mentation of their mass, due to the surrounding element, owing to the 
high density of the salt water. The fact serves as a proof that, in com- 
paring young individuals of Art. milhausenit with individuals of Art. 
salina of the same age, we find the appendages in the former of con- 
siderably larger size. Only a much earlier state of growth of Art. salina 
relatively agrees with the later state of age of those individuals, bearing 
the characters of Art. milhausenti, inhabiting salt water of much higher 
density than Artemia salina. Beside the interesting changes occurring 
during the course of development of generations influenced in a known 
manner by the surrounding element, we here observe an accession and, 
as it were, an accumulation of mass in the known parts reacting upon 
the element and developing according to the demands of this element. 
I call this a direct influence of the surrounding element, and moreover 
such an influence, toward which the organism keeps active, and I dis- 
tinguish it from another likewise direct influence of the same element, 
toward which the organism, so to speak, passively submits. As an ex- 
ample of this latter influence, I mention the retrograde development of 
the abdominal furca of Art. salina in salt water of high density, whereby 
the furca becomes as if atrophied, and, indeed, independently of the 
sexual maturity in specimens, appearing earlier than the full develop- 
ment of the body-parts. That influence of the element upon which de- 
pends the change of form, owing to the changed point of appearance of 
sexual maturity, I call the immediate influence oft the surrounding 
element upon the organism. In Artemia, and also to some degree in 
1 “Zur Kenntniss des Baues und der Entwicklung von Branchipus stagnalis und 
Apus cancriformis.” In the ‘‘Abhandlungen K. Ges. der Wissensch. zu Gottingen.” 
Vol. XVIII, 1873, p. 19. 
2 “Zur Kenutniss von Branchipus stagnalis.” Zeitschrift f. w. Z., vol. xxv, 1st 
supplemental part, pp. 23 and 37, 
