Anatomy of Notorycfes typhlops. 89 



posterior part of the Organ, descending anteriorly to the mesial 

 wall, as seen in transverse sections (Fig. 6, n.f.). 



Minute Structure of Jacohsoti' s Organ. 

 For convenience of description we may take first the lateral 

 wall, with the structures outside this, and then similarly the 

 median wall. 



1. — The Lateral Wall. 



The epithelium lining the Organ of Jacobson on this side 

 (Fig. 6, l.w.) is .04 to .06 mm. thick, being slightly less than in 

 the Dog, and the same as in the Guinea-pig and Rabbit. Tt con- 

 sists of a columnar epithelium, similar to that lining the nasal 

 cavity (which is .06 mm. thick), having here apparently two layers 

 of cells ; (a) an outer columnar layer with long, strong cilia 

 {c.f., Guinea-pig and Dog, and contrast the Rabbit), and oval 

 nuclei. These are interspersed with goblet cells, which 

 are numerous in parts of the lower half of the wall ; 

 (/?) an inner layer with rounded nuclei. It will be seen 

 that this differs from that of the Guinea-pig as described by 

 Klein^ in that his middle layer of spindle-shaped cells is not 

 visible here. Probably this is due to the fact that all the material 

 at my disposal is spirit-hardened, and in such cases Klein has 

 found great difficulty in distinguishing the spindle-shaped cells 

 from those of the columnar layer. Next to this is a well-marked 

 fibrous layer corresponding to the subepithelial layer of other 

 forms, with blood vessels and gland alveoli. The cavernous tissue 

 shown by Klein to be so well developed in this position in the 

 Guinea-pig^ and Rabbit,'^ and by Broom in Phascolarctos,' and in 

 Petauroides,* does not exist here in Notoryctes, the blood vessels 

 of this side being limited to an artery (o), running longitudinally 

 along the middle line of the tube, and one or two small veins. 

 This is more like what we find in the ordinary Marsupials, which 

 have a single hilar blood vessel. It may be seen in Macrosce- 

 lides,"* and is much greater in extent than in the lateral wall of 



1 Q.J.M.S., vol. xxi., p. 101-3. 



2 Loc. cit. p. 563-4. 



3 Proc. Linn. Soc. N.S.W., vol. xi., n.s., 1896, p. 613. 



4 Loc. cit., p. 607. 



6 Proc. Zool. Soc, 1902, vol. i., p. 226. 



