20 SUMMARY OF CURRENT RESEARCHES RELATING TO 



probably date back to a very early post-Cynodont stage of a Mammalian 

 evolution, and their absence in Monotremcs is a derivative feature asso- 

 ciated with the transformation of the jaws. 



The development or deficiency of vibrissas is doubtless correlated 

 with the mode of life. Pocock calls attention to some noteworthy 

 points. There is a deficiency or complete absence of vibrissas in all the 

 ant-eaters, like Echidna, Tamandua, and Mania, quite unrelated genera. 

 They are highly developed in thickness and length in piscivorous 

 aquatic or semi-aquatic genera like Ghironeetes, Potamogale, Lutra, and 

 ( 'ynogale, and they are comparatively feeble or deficient in aquatic Her- 

 bivores, like the Sirenians, Hippopotamus and Hydrochcerus. The 

 Polar Bear is exceptional among predatory aquatic Carnivores for the 

 poor development of the vibrissas, but its ancestors had probably lost 

 them before they took to the water. In the Primates they dwindle 

 from lower to higher types, and this is probably correlated with the 

 gradual perfection in the use and sensitiveness of the hand. They are 

 highly developed in active aboreal species like squirrels, and reduced in 

 size and number in slow climbers like sloths (Bradypus), Pottos (Pero- 

 dicticus), and the tree-kangaroo {Dendrolagus ur sinus). They are 

 generally prevalent in the smaller burrowing, bush-frequenting, or forest 

 species among Eodents, Carnivores, and others. They are decadent in 

 larger forms like the Ungulates. 



■*■&" 



Organ of Jacohson and Palatine Cartilage.* — A. Arnback Christie- 

 Linde describes the structure of the organ of Jacobson in Sorex, 

 Crocidura, Tupaja, and other types. It is relatively complicated in Tupaja 

 and Gymnura, but it is possible that this may be due to a difference of 

 sex. It is probable that the Insectivora are descended from Vertebrates 

 in which the organ of Jacobson was of a more complicated structure 

 than is now T generally met with in Mammals (excepting Monotremes). 

 The same type of Jacobson's organ occurs in widely different groups. 



The cartilago palatina lies between the palatine processes of the 

 premaxillas and maxillae. It is most probably homologous with the pro- 

 cessus palatinus of Gaupp in Echidna. It belongs to the primordial 

 cranium, and is originally a process from the floor of the cartilaginous 

 nasal capsule into the region of the secondary palate. It is present in 

 Lacertiha. It is rudimentary in Tupaja, Macroscelides, Sorex, Lepus, 

 Bats, Lemurs, and higher Mammals generally. 



Rate of Growth in Marine Invertebrates.! — J. H. Orton publishes 

 a preliminary note on an investigation into the rate of growth of marine 

 Invertebrates which he began in 1911. The particular objects of his 

 research are : to establish the age of common marine Invertebrates ; to 

 determine the minimum age at which these forms begin to breed ; to 

 examine the rate of growth at different seasons of the year and under 

 different conditions ; and to investigate as far as possible the fecundity 

 of different forms. He finds that the rate of growth in many forms is 

 much more rapid than has been suspected. Thus many species of 



* Morphol. Jahrb., xlviii. (1914) pp. 343-64 (14 figs.). 

 t Journ. Marine Biol. Assoc, x. (1914) pp. 312-36. 



