PACKARD.! TRANSFOEMATION 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. e., the 

 surface 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 little-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 milliaiisenii^ not only owing 

 to retained growth of A. salina^ whose younger specimens have larger 

 appendages, but also in consequence of tlieir accession^ owing to aug- 

 mentation of thsir 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. milhausenii 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 chanicters of Art. milhausenii, inhabiting salt water of much higher 

 density than Arfsmia salina. Beside the interesting changes occurring 

 during the course of development of generations inlluenced 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 1 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 of the surrounding 

 element upon the organism. In Artemia, and also to some degree in 



1 "Zur Keuntniss des Baues und der EntTv-ickliiDg von Branchipus stagnalis und 

 Apus cancriformis." In tlie " Abliandlungen K. Ges. der Wissenscli. zu Gottiugen." 

 Vol. XVIII, 1873, p. 19. 



" "Zur Kenutniss von Branchipus stagn alls." Zeitschrift f. w. Z., vol. xxv, 1st 

 supplemental part, pp. 23 and 37. 



