SCHIZOPOD TROM TASMANIA. 295 



segment, lying close to the dorsal surface and tapering gradually at both ends into a 

 more slender cylindrical vessel. I have traced the whole tube from about the third 

 thoracic segment back jxxst the posterior intestinal cfecum. Of the arteries passing from 

 the heart, exclusive of its anterior and posterior prolongations, which may be considered 

 respectively as the cej)halic and upper abdominal arteries, I have succeeded in tracing 

 only one prominent artery passiiig almost vertically downward between the seventh 

 and eighth thoracic segments, which probably su^jplies the greater portion of the sternal 

 region. But I have failed to find any trace of the valvular openings into the pericar- 

 dial sinus, by which the blood returning from the branchite and other portions of the 

 body is again fed back to the heart. This is of course due to the very imperfect 

 condition of the tissues examined. 



The branchiie, as already mentioned, are all lamelliform and are carried externally. 

 Morphologically there are seven pairs on each side, but those of the first pair of legs 

 (maxillipeds) are very much reduced in size, and probably more or less in function also. 

 The branchia-like cndopodites of the abdomiual appendages are no doubt f unctionless as 

 breathing-organs. 



Reproductive organs. — I have not succeeded in definitely making out tiu; structure of 

 the testes and vasa deferentia in the very few male specimens at my disposal. The male 

 organ, so far as it was identified, consists of two thin, whitish tubes, lying nearly parallel 

 one to another, above and slightly on each side of the intestine (PL XXVI. fig. 5). These 

 extend from the third segment of the thorax, where they are smaller and very mu.ch 

 twisted, as far Ijack as the telson. The densely-twisted part of the organ lies in the 

 penultimate segment of the thorax. The vasa deferentia pass outward from the body- 

 cavity by two rather wide tul:)es, which come down near the outer side of the body to 

 the first pair of abdominal legs. 



Tlie ovaries form a somewhat flattened pinkish mass on each side of the body above 

 the alimentary canal, having rounded lobes projecting upward and downward so as 

 almost to meet in the median line. The supra-abdominal artery lies along the margins 

 of these lobes, which extend from the last segment of the thorax to the region of the 

 posterior intestinal caecum. In more sexually mature specimens in w liich the ova were 

 found lying in the oviducts, the latter were seen to lie lower down in the body-cavit}^ at 

 the sides or even below the intestine. In the most advanced specimen examined the 

 ova were nearly one millimetre long and were oblong in form. Even in such relatively 

 well-developed ova there was no commencement of differentiation into definite structures. 

 The whole interior appeared to be composed of more or less spherical cells, which were 

 especially densely packed and were smaller in size towards the centre. Even at this 

 stage, the ovum had a strong, homogeneous, well-defined wall, and appeared as if nearly 

 ready to be extruded. In one specimen I found ova ranging from an early morula (?) 

 stage up to the form described, but all the tissues were in bad preservation. I have not 

 succeeded in tracing the ovaries down to the genital opening, which is on the sternum, 

 between the last two pairs of thoracic legs. 



39^ 



