678 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



nearly the entire length. They are indistinct anterior to the nuchal gland 

 but are usually conspicuous from that point to the anus. The median 

 interspace between the bands corresponds to nine longitudinal muscle 

 bundles, the bands themselves to five each (they are formed of six lines 

 of pigment cells corresponding to six intermuscular lines), and the dis- 

 tance separating them from each margin to eleven. 



Annulus ai of each somite from VI to XXVI inclusive is much more 

 heavily pigmented than the others, and the pigment is especially aggre- 

 gated on its posterior half, the b2 constituent. Thus in such typical cases, 

 the dorsum is marked by well-defined, narrow, metameric, transverse bands, 

 which become fainter anteriorly, where they can seldom be traced beyond 

 VI, and altogether diffuse posteriorly on XXV and XXVI. These trans- 

 verse bands extend the entire width of the dorsum, both mesiad and 

 laterad of the longitudinal stripes. Other examples are less typical and 

 show the pigment spreading over aj as well as bi, but the former never 

 becomes so dark and is brown rather than blackish ; a2 always remains 

 paler. The characteristic pattern is due to black pigment cells deep- 

 seated between the muscle bands. 



Reproductive Organs. The male pore is situated at ~X.\\aila2 y the 

 female at XII a2la^. The former is the more conspicuous, and in some 

 specimens, but not in the type, is in the center of an elliptical disc, which 

 is wedged between the two contiguous annuli. There are six pairs of 

 testes (Plate XLIX, fig. 10) of globoid form alternating with the gastric 

 caeca and filling up the spaces between these. Dorso-ventrally they are 

 deeper than the caeca, reaching the same dorsal level, but extending to a 

 lower ventral one. Though inter-metameric in position, they probably 

 belong to the somites in which their posterior halves lie, consequently to 

 XIV to XIX inclusive. The vasa efferentia and vasa deferentia are 

 excessively delicate and can be traced only with difficulty. The vas 

 deferens of each side passes dorsad of the caeca and mesiad of the testes. 

 Reaching the posterior end of XII, it bends sharply mesiad, traversing 

 muscles and pharyngeal glands ventrad to the ducts of the latter, and 

 reaches the ventral sinus, through which it extends caudad, increasing, 

 first abruptly and then gradually in diameter. The change from the 

 minute vas deferens to the larger epididymis takes place in XIII. The 

 long epididymal loop (sperm sac) thus formed is very conspicuous, 

 reaching to the posterior end of XIX, and, being considerably convoluted 



