REPORT ON THE GREEN TURTLE. 47 



of sutures running from the nose to the superoccipital. In the mandible an important 

 change takes place, for the articular part of the cartilage becomes ossified, endosteally, 

 and then coalesces to some considerable degree with the ectosteal " articulare." 



This determines the name of that outer plate, what might in younger specimens be 

 thought to be a mere splint like the others in this part ; so also in highly-ossified 

 Batrachia, as the " Aglossa," the bone, which was taken for the " angulare " by Huxley, 

 coalesces with the endosteally ossified articular region of the free mandible. 



The post-mandibular arches merely increase in size, and not in character. 



The rapidity with which this type undergoes its metamorphosis, even in an early 

 period of its life within the egg, is very remarkable as compared with what is seen in the 

 Batrachia with their large larvae. 



But in Pipa, which scarcely shows a trace of even external gills, the metamorphosis 

 is nearly if not quite as rapid, and, at extrusion, the young are as perfect as newly-hatched 

 Turtles ; in Dactyletkra we may see that, as to the skull, there is but a step between a 

 Batrachian and a Chelonian. 



There is one thing to be noted of great importance in the development of the Turtle, 

 and that is the number of its body-segments at various stages, their rapid increase at 

 first, and then the suppression or extinction of several, afterwards. 



In embryos a Little more than a cjuarter of an inch in length (first stage), there are 

 about twenty-seven muscle-plates or somatomes. 



In embryos ranging from 6^ to 9 lines (a little more than half, to three-quarters of 

 an inch), there are fifty-one of these divisions of the body visible externally. 



Now in the adult I can only find forty-one developed vertebrae, viz., 8 cervical, 10 

 dorsal, 2 sacral, 21 caudal — 41 in all. 



But in the third and fourth stages there are at least 15 somatomes in the cervical 

 region, in the dorso-lumbo-sacral 12 (as in the adult), and 24 in the caudal— 51 in all 

 (see PI. I. figs. 3 and 7) ; thus we miss in the adult 7 in the cervical and 3 in the 

 caudal — 10 in all. 



This free suppression of segments suggests a great secular modification by shortening 

 of a form not unlike a Plesiosaur. 



Summary. 



First Stage. 3 J lines long. — In this stage there is nothing to distinguish the embryo 

 from that of a Snake, Lizard, or Bird. There are twenty-seven somatomes ; the heart is 

 looped ; there are four clefts, of which the fourth is scarcely open ; the limbs are 

 appearing as thickenings ; the rudiments of the sense-capsules are very distinct, that of 

 the ear being especially remarkable for the clearness of its lipped opening ; there, is a 

 slight rudiment of the maxillo-palatine fold (PI. I. fig. 1). 



