THE SYSTEMATIC ANATOMY OF A FCFTAL SKA -LEOPARD. 469 



varieties, vi/. a majority which stain lightly, and here and there isolated cells 

 staining intensely ; the cytoplasm of the latter cells is also more granular in 

 appearance. In the fully formed gland these deeply staining cells are more 

 numerous, and collected into small groups instead of being isolated cells. The pro- 

 liferating columns seen in Rathke's pouch are composed of rather cuboidal, or in 

 some cases columnar, cells, which do not possess any special affinity for eosin, but 

 the nuclei of which stain deeply with basic dyes ; no evidence of the syncytial 

 structure seen in the pars intermedia of later stages is to be made out, nor does any 

 colloid appear to have been formed as yet. The pars nervosa appears to possess 

 much the same minute structure as does that part of the adult gland ; for the most 

 part, neuroglia cells and fibres predominate, some of the former being spindle-shaped 

 and occurring in that portion of the lobe which lies next the epithelium forming 

 the roof of Rathke's pouch, their long axes being at right angles to the ventral 

 surface of the lobe. The portion of the cavity of the 3rd ventricle which passes 

 into the infuudibulum is lined by an epeudyma of the usual type, viz. rather high 

 columnar epithelium, the component cells being ciliated, whilst the basal portions 

 of these cells are continued as neuroglia fibres into the substance of the pars nervosa. 

 There is no colloid to be detected as yet in this part of the pituitary, although in the 

 fully formed gland small particles of colloidal material derived from the pars inter- 

 media are to be seen scattered throughout the posterior lobe. Lying just dorsal to 

 the infuudibulum is a folded portion of the floor of the 3rd ventricle, which encloses 

 a small fold of pia mater ; this portion later on becomes modified to form a small 

 ovoid mass lying on the dorsal aspect of the posterior lobe, and contains syncytial 

 strands of nucleated cytoplasm more fully described by the author in a previous 

 communication.* When fully formed it is very vascular, but its functional signi- 

 ficance is not at all obvious. The above somewhat brief description of some of the 

 developmental aspects of the pituitary of the Sea-Leopard Seal are, of necessity, 

 incomplete, on account of the fact that only a single specimen was available for 

 investigation. It would be interesting to follow some of the earlier phases, inasmuch 

 as the gland appears in this animal to have a high functional significance quite as 

 much so, in fact, as in some higher types. t 



GENERAL COMPARATIVE CONCLUSIONS IN CONNECTION WITH THE ANATOMICAL AND 

 HISTOLOOICAL FEATURES PRESENTED BY THE FOETUS OF STENORHYNCHUS. 



(i.) The ftL'tus, in the light of the above considerations, shows many points in 

 common with the human fu-tus at the beginning of the fourth month of Ultra-uterine 

 development. If the relative rates of growths during the earlier developmental 



* !>,,. rll. 



t For further details of the cytological characters of the various regions of the mammalian pituitary, see 

 Sm AKKH, " Text-Bonk of Microscopic Anatomy " (< t >imin's Anatomy, vol. ii. part i.). 



(ROY. soc. KDIN. TRANS., VOL. L., 247.) 



