428 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



Fig. 2. Transverse section through the body of the same animal some distance behind the ganglia. 

 The sheath for the proboscis now separates the latter from the oesophagus, which has 

 attained a considerable size. The lateral nerve-trunks have nearly reached their proper 

 position, viz., to the inner side of the internal muscular layer of the body-wall ; s, granular 

 masses at the sides of the oesophagus. x 55 diameters. 



3. Isolated gland-cells from the posterior chamber of the proboscis. x 350 diameters. 



4. Transverse section through the anterior region of the proboscis in a large 0. alba, after 



hardening in spirit and mounting in chloride of calcium; a, central cavity; b, the papillary 

 glandular layer; c, internal circular muscular coat; d, inner longitudinal layer ; g, pecu- 

 liar reticulated or beaded layer ; /, external longitudinal muscular layer ; g, external 

 layer; h, basement-layer. x 90 diameters. 



5 . Transverse section through the stylet-region of the proboscis of the same species, in the 



line of the lateral sacs. x 350 diameters. 



6. Glandular papillae from the proboscis of Tetrastemma vermiculus, seen on the free edge of 



the everted organ, x 700 diameters. 

 7- Glandular papilla? in the anterior region of the proboscis of O. alba, seen in the ordinary 



condition of the organ under pressure. x 210 diameters. 

 ... 8. Portion of the everted inner surface of the posterior chamber of the proboscis of the same 



species. The glands have for the most part burst and become minutely hirsute, x 350 



diameters. 

 9. Portion of the glandular surface of the postei'ior chamber of the proboscis in its normal 



condition. x 350 diameters. 

 ... 10. Portion of the inner surface of the same chamber, viewed in situ under pressure. The 



papillae are hirsute, and their contents scattered over the surface of the organ. x 350 



diameters. 

 ... 11. Lanceolate and pedicled papillae from the anterior part of the proboscis of T. vermicuhis. 



x 300 diameters. 

 ... 12. Central stylet of Ommatoplea purpurea,. x 700 diameters. 

 ... 13. Central stylet and basal apparatus of the same species. x 350 diameters. 

 ... 14. Developing or recently repaired central stylet-apparatus in T. algce. x 700 diameters. 

 ... 15. Stylet from a lateral sac of the same animal. x 700 diameters. 



Plate VI. 



Fig. 1. Head of O. alba. x 210 diameters. 



2. Proboscis of the same species, gently but completely extruded under chloroform, so as to 



render the central stylet prominent. x 55 diameters. 



3. View of the nervous and circulatory systems in the anterior end of 0. alba. 



4. Abnormal stylet-region in the same species ; a, perfect stylet-sac of the left side ; b, shrivelled 



sac of the right side. x 210 diameters. 



5. Stylet-region of the proboscis of T. varicolor, with the reservoir somewhat contracted, x 210 



diameters. 



6. Extremity of the posterior chamber of the proboscis in T. cariegatum, apparently after 



rupture of the muscular ribands from the sheath of the organ. x 350 diameters. 



7. Stylet-region in Ommatoplea melanocephala. x 90 diameters. 



8. Circulation, &c, in the posterior end of O. alba; a fragment of the same drawing from which 



fig. 3 was cut. 



9. Isolated lateral stylet-sac of O. alba ; a, a few fibres which probably act as constrictors of 



the aperture of the duct. The laminated arrangement of the calcareous layers of the 

 stylets is indicated in this figure. x 350 diameters. 



... 10. Tip of the snout of Borlasia olivaeea, with proboscis partly protruded. x 210 diameters. 



... 11. Central stylet-apparatus in Ommatoplea pulclira ; a, central stylet; b, reserve-stylet in situ. 

 x 210 diameters. 



... 12. Central stylet and its basal granular apparatus in O. gracilis, turned round so as to demon- 

 strate the curvature of both. x 100 diameters. 



... 13. Isolated central stylet of the foregoing. x 420 diameters. 



