COMMON CRAYFISH. 181 



of many other animals as well. Tetronerythin is a pigment commonly distributed 

 in the animal kingdom and is found in various tissues, e.g. in the integument and 

 muscles. It has been supposed by Merejkowski to have a respiratory function, but 

 this is doubtful. The yellowish-red granules, seen sometimes in the blood-corpuscles 

 of Decapod Crustacea, are perhaps formed of it. 



Heart. Bela Dezso, Z. A. i. 1878. 



Circulatory System. Astacus, Krohn, Isis, 1834. Stomatopoda, Schizopoda 

 and Decapoda. Glaus, Arb. Zool. Inst. Wien, v. 1884. 



Structure of -vessels, &c. Haeckel, M tiller's Archiv (Archiv f. Anat. und Phys.), 



1857- 



Blood of Decapod Crustacea. Halliburton, Journal of Physiology, vi. 1885. 

 Haemocyanin and Tetronerythrin, ibid. On the latter see also Merejkowski, Bull. 

 Soc. Zool. France, viii. Haemoglobin in Crustacea, see lists in Halliburton, op. cit. ; 

 also van Beneden on Lernanthropus, Clavella, and Congericola. Bull. Acad. Roy. Sc. 

 Belgique (2), 49, 1880; Id. Z. A. iii. 1880. Myohaematin. MacMunn, P. R. S. xxxix. 

 1885. 



35. COMMON CRAYFISH (Astacus ftuviatilis), 



Dissected so as to show its digestive, reproductive, and respiratory systems in situ. 



THE greater part of the tergal region of all the segments of the body 

 has been removed, together with the heart and its vessels and in the 

 abdomen the thin stratum of extensor muscles. The stomach occupies 

 a central position anteriorly, and is clearly divisible into a wider cardiac 

 portion in front and a narrower pyloric portion behind. An arcuate 

 plate, the 'cardiac ossicle,' crosses the cardiac portion at the point of 

 greatest width, and receives the insertion of the major part of the anterior 

 gastric muscles which spring from the base of the rostrum. A pyloric 

 ossicle crosses the pyloric portion of the stomach in a similar manner, 

 and gives attachment to the posterior gastric muscles which take origin 

 posteriorly from the carapace. The other stomachal ossicles can only be 

 studied when the stomach is properly opened. To the right side of the 

 pyloric portion of the stomach is seen the end of the adductor mandibulae 

 muscle separated from its attachment to the carapace ; and behind it, as 

 well as to either side, are the two lobes of the liver. On the left side, 

 in front of the liver, is to be seen a small portion of the sac of the 

 green gland. The paired anterior lobes of the testis lie in the middle 

 line between the liver lobes. The azygos posterior lobe overlies the 

 intestine. At the spot where these three lobes unite the right and left 

 vas deferens take origin as slender tubes, the calibre of which rapidly 

 widens. They are disposed in many convolutions which intrude some 

 way into the abdominal cavity before they turn downwards, to open on the 

 coxopodites of the last pair- of thoracic limbs. The intestine takes a 



