36 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
on the cephalic side of the oral plate, and is, therefore, of epiblastic 
origin, as is also the processus infundibuli. Both of these outgrowths 
are the direct result of cell-proliferation. When further developed and 
united the two form the structure known in adult mammals as the 
pituitary body, and are assisted by the proliferation of cells from the 
mesoblast. 
Development of Wolffian Body in Chick and Rabbit.*— Prof. J. 
B. Haycraft has a preliminary notice of his investigations. The first 
sign of the developing duct is a solid growth, which only later becomes 
differentiated from the rest of the mesoblast, and which runs in the length 
of the embryo. It is joined at each segment to the walls of the body- 
cavity by equally solid columns of cells — the primitive segmental 
tubules. The author can find no evidence that the tubules form first, 
and then join the Wolffian duct, as has been frequently described. A 
central cavity appears to be formed between the cells. It sometimes 
happens that, in a section, a tubule is seen with apparently a free end 
detached from the duct ; this is because the tubules bend, and are often 
cut across at a bend ; if these tubules are traced out in other sections of 
the series they can invariably be traced to the duct. Prof. Haycraft 
finds that there are no secondary tubules arising from those first formed, 
in the chick or rabbit, though, it is true, they have often been described. 
Dentition of Pinnipedia.| — Prof. W. 
Kiikenthal gives an account of 
In the foetal 
the development of the teeth in the walrus and the seal, 
walrus the dental formula is — — J — — — J — - 4 
Two of the 
3_3, 1—1, 3—3, 1—1 
incisors above and three below disappear, the permanent lower canine 
becomes like a premolar, the upper forms the well-known tusk, the three 
premolars are replaced, the molars disappear. Thus the formula for the 
1 ] 1 2 3 3 
adult dentition is — - — — - — . There is in the walrus, when 
U, 1 — 1, o — o 
compared with other Pinnipedia, a characteristic shortening of the jaw, 
in adaptation, the author thinks, to the habit of mussel-crushing instead 
of fisli-catching, and the well-worn appearance of the premolars is due 
to the fact that the upper and lower teeth grind against one another and 
do not alternate as in other Pinnipedia. In consequence of the shorten- 
ing of the jaw there is in the upper jaw a fusion of the two molar rudi- 
ments, which are originally quite distinct. 
Of the seals, PJioca groenlandica has been especially investigated. 
The milk dentition, almost wholly absorbed in intra-uterine life, is 
3 — 3, 1 — 1, 4—1 
2 — % 1 - 1 , " 
thal, belong 
3—3, 1—1, 5- 
^ ^ , with two molars, which, according to Kiiken- 
essentially to the first set. The adult dentition is 
—5 
The lateral tubercles of the back teeth are late in 
2 — 2 , 1 — 1 , 5—5 
developing. Hints of no less than four successive dentitions are found 
* Anat. Anzeig., xi. (1893) pp. 75-9 (6 figs.), 
f Jenaische Zeitschr. f. Naturwiss., xxviii. pp. 76-118 (2 pis.), 
j It seems to us that in the formula on p. 92 there should be three incisors 
instead of two. 
