The Origin of Mammals. 



87 



Fig. 18. Eight days' incubation, showing commencing segmentation in the fourth 

 generation. 



Fig. 19. Nine days' incubation, showing sporulation in the fourth generation. 

 Fig. 20 shows a young merozoite of the fifth generation after 10 days' incubation. 



All of the above figures were obtained from one culture tube, without the removal 

 of leucocytes and without the addition of fresh serum or corpuscles. 



Fig. 21 shows a young benign tertian parasite at the time of inoculation of the culture 

 tube. 



Figs. 22, 23, and 24 represent 8 hours' grow T th in culture tube at 39° C. 



Figs. 25-30 show parasites obtained from the culture tube after 20-29 hours' incubation. 



Fig. 30 is a female gamete (undivided chromatin and scattered pigment) found in the 

 culture tube ; similar gametes were found in the blood at the time of inocula- 

 tion of the cultures, so it is probable that this gamete was one of these, and 

 that it had not developed in the culture. 



Note the large size of the corpuscles in the benign tertian as compared with those in 

 the malignant tertian, also the Schuffner's dots and the scattered pigment. The 

 spores also are larger and fewer in number in the case of the benign tertian parasites. 



CROONiAisr Lecture : The Origin of Mammals. 

 By Dr. Robert Broom. 



(Lecture delivered June 5, 1913.) 



(Abstract.) 



An endeavour is made to trace the evolution of mammals from Cotylosaurian 

 ancestors through the carnivorous Therapsida. In Upper Carboniferous times 

 the line probably passed through some primitive generalised Pelycosaurs ; in 

 Lower Permian through primitive, probably Therocephalian, Therapsids. In 

 Middle and Upper Permian the line passed through the Gorgonopsia. In 

 Triassic times the mammalian ancestors were small generalised Cynodonts. 

 In Lower Jurassic the mammals are so Cynodont-like, and the Cynodonts so 

 mammal-like, that in no single case are we absolutely certain which is 

 which. 



In the Therocephalia, the Gorgonopsia, and the Cynodontia, the skull is 

 very mammal-like. The zygomatic arch is, as in mammals, formed by the 

 jugal and the squamosal. The teeth are divided into incisors, canines and 

 molars. In the later Gorgonopsians there is an imperfect secondary palate : 

 in Cynodonts a complete secondary palate as in mammals. In Permian 

 Therapsids there is a single occipital condyle ; in the Triassic Cynodonts 



