COMPAliATIVE MOliPHOI.OGY OF THE GALEODID.E. 417 



the digestive tubules) . On the left, the visceral membrane is held down dorsally and raised 

 vcutrally by muscle-fibres, the " veno-pericardial " muscles. The blood-space below and 

 the pocket above are the remains of the original inter-diverticular spaces [cf. fig. 5). 

 Dv, portion of a dorso-ventral muscle. 

 Fig. 10. A portion of the main duct of the coxal gland in G. arahs, highly magnified. The connective- 

 tissue envelope contains blood-lacunse [b) and tracheie {tr) ; a group of the gland-cells are 

 seen with dividing nuclei deeply stained, in the other cells the nuclei are vesicular. 



11. A few cells of the same more highly magnified, the nuclei measured by eyepiece micrometer. 



11 a. A dividing, deeply-stained nucleus, with measurements. 



12. A section of the main duct of the coxal gland near the aperture ; the cells are less differentiated, 



13. A portion of the spongy mass of tubules developed at the proximal end of the main duct of 



the coxal gland {cf. PL XXXI. figs. 4, 5). 



14. Portion of the same, highly magnified, be, blood coagulum ; /, tracheae ; p, large solid masses 



of protoplasm (? cells) traversed by tracheal tubes. 



15. The genital and stigmatic opercula of a specimen of Rhax Kvyserlingii, Pocock (in the British 



Museum), g', anterior aperture (?), which may be the genital aperture; g", the ordinary 

 position of the genital aperture into which the cement-glands open ; stig, the positions of the 

 stigmata; cf. the sequence ^^, stigi, stig, (Plate XXIX. fig. 11). 



16. Portion of a transverse section through an ovary, ep, ovarial epithelium ; m, felt of muscle- 



fibres ; /, trachea ; /, follicular membranes, the one on the left is shrunk after the tUscharge 

 of an egg; em, egg-membrane showing two zones ; y, yolk-granules. 



17 A, B. Diagrams to compare the initial modifications of the anterior segments. A, of the 

 Arachnids; B, of the Crustacea and Merostomata ; p, prostomium. 1, 2, 3, 4, the 1st four 

 segments. In A a sucking-beak results, while in the latter the appendages can function as 

 jaws round or within the mouth. 



18. Diagram showing in transverse sections the origin of the limbs and tracheaj (or glands) of the 

 three chief divisions of the Arthropods, from the parapodia and setiparous glands of a 

 Chsetopod Annelid. A, Crustacea; B, Arachnida ; C, Hexapoda. d, dorsal; v, ventral 

 branch of the parapodium; a, acicular gland; g, gill; p,v, exopodite ; c, sensory cirrus 

 (tf. text, pp. 403-404). 



SECONU SERIES. — ZOOLOGY, VOL. VI. 55 



