512 GEOLOGICAL SURVEY OF THE TERRITORIES. 



precedinjj segments in old specimens, are more prolonged than in young 

 ones. With the fnrca is the last abdominal segment usnally a little 

 longer than the double length of the penultimate segment, however 

 sometimes also a little shorter, AThich probably depends upon the age 

 as well as upon tLie surroundings. I have yet to add that the longer 

 the abdominal furca in the Horm A^'temia is, the shorter appears the last 

 abdominal segment; it is as if the furca develops on account of this 

 segment, especially on account of the second half behind the sensory 

 bristles (which are nearly in the middle of its length). This answers the 

 circumstance, that in the species BrancMims^ with usually great length 

 of the abdominal appendages, the last abdominal segment is consider- 

 ably shortened, as the abdominal segment, which corresponds to that 

 part of the last abdominal segment in Artemia, which part is behind the 

 last sensory bristles, i. e., behind that part where Artemia lacks the ar- 

 ticulation, which exists in Branchipiis {excei[)tmg Branchipvs stagnalisf). 

 Kegarding the circumstance that the last apodous abdominal segment 

 of Artemia is homologous with the two last, *. e., the 8th and 9th apodous 

 segments of Branchipus, we must firstly realize the disposition of the 

 sensory bristles on the abdomen of the species Artemia and BrancMpuSy 

 and secondly the origin of the articolation in the middle of the last x>ro- 

 longed segment of Artemia^ ininicdiately behind the sensory bristles, in 

 the domestication of the entire generations of these animals in continually 

 diluted sa-lt water. On each apodous abdominal segment of the Branchi- 

 pidw the sensory bristles are at the end of the segment before the artic- 

 ulation; the last segment makes an exception, which has no sensory 

 bristles before the abdomiiurl apx)endages. The Artemia show an 

 equal disposition of sensory bristles on the postabdomen, with the sole 

 exception that such bristles are also on the last (eighth apodous) prolonged 

 segment, about in the middle or above it. As into the sensory bristles, 

 located about in the middle of the iast prolonged (eighth apodous) seg- 

 ment in Artemia^ enter likewise nerve-branches, as is the case with 

 those at the end of the preceding segments, and the sensory bristles 

 at the end of the segment in Branchipus (therefore also into those at the 

 end of the peiuiltimate segment), it follows that the first half of the last 

 segment (eighth apodous) in Artemia corresponds icith the tchole penultimate 

 (eighth apodus) segment of Branchipus, while the second half of this 

 segment (eighth ajjodous) in Artemia is homologous with the last (ninth 

 apodous) segment in Branchipus. As I do not write a monograph of a 

 Si)ecies, and as for me only the disjiosition of the sensory bristles was 

 of importance, I cannot give the number of bristles on each ai)odoas 

 abdominal segment. Sometimes 1 found only two bristles on the seg- 

 ments, sometimes four, circularly distributed around the segment). I 

 only know that these sensory bristles also exist at the end of the two 

 first apodous segments opposite the external sexual organs, and also at 

 the end of the last limb-bearing segment, likewise also on the other 

 segments of this body-part. Spangenberg found in Branchipus stagnaUs^ 

 sensory bristles by twos on the abdominal segments, and only on the 

 eighteenth, being the seventh apodous segment, he found four bristles. 

 It is without doubt, that in Branchipus stagnalis, in case it has only eight 

 apodous segments, the sensory bristles are not at the end of the eighth 

 apodous segment, but before the faint articulation of this segment, 

 which is figured by Olaus,^ or if Branchipus stagnalis should, like the 

 other species possess nine segments on the end of the eighth segment. 



^Zeitscbr. f. wiss. Zool., vol. xxv, supplem. p. 28. 

 '■^Loc. cit., Plato V, fig. 16. 



