214 THE DEVELOPMENT OF THE TADPOLE. 



yi$ grains ; on July 19th, 2 '8 grains ; on July 24th, 275 grains ; 

 and on July 26th, 2 '6 grains. In this case the loss was enormous, 

 and finding that the little creature which I had watched so care- 

 fully for many months was daily losing flesh because it could not 

 find foot to eat in my place, and having now become a perfect 

 frog I took what I conceived to be the most humane course, and 

 turned it out to grass, losing sight of it for ever. 



To return, however, to the development of the limbs. By the 

 end of the first week in June the bones of the pelvis are seen to 

 be well formed, portions of them being shewn in Fig. 7, PI. XXII. 

 A transverse section, of June 10th, shews also that the long thin 

 bone, called the urostyle, attached in front to the vertebral column 

 and behind by means of cartilage to the pubis, has also commenced 

 to form. It must not, however, be supposed that these structures 

 are yet true bone. They are merely cartilage, or if bone at all, 

 then so soft as not to injure the edge of a keen razor whilst 

 cutting. The bones of the head appear in a much higher state 

 of development, and offer a distinct resistance in cutting. By the 

 beginning of July many animals were outwardly perfect frogs, and 

 sections taken at this period through the whole animal present a 

 most ludicrous appearance on the slide, looking very like a 

 miniature caricature of the human body. In these the muscles, 

 with their attachments to the bones, are beautifully seen. Some 

 of them in the hind-limbs I have tried to delineate in the plate. 

 On the slide each muscle fibre stands out distinct and clear, many 

 of them yet unstriated, but each muscle distinct from the rest, 

 ultimately connected with its own special portion of the perios- 

 teum, now seen as a very fibrous structure. The bone-cells now 

 consist of two kinds — (i) Large cells, with small nuclei; 

 (2) Small cells, with comparatively large nuclei. The former 

 constitute the mass of the bone, whilst the latter form the 

 articulations. Here they appear to be interpenetrated by the 

 fibrous periosteum, which may possibly account for the property 

 of articular cartilage splitting up vertically. The under portion of 

 the skin of the thigh is only very loosely attached to the muscles 

 beneath, and is supported mainly by a fibrous attachment, which 

 connects it with the point of the pubis. 



As previously mentioned, the development of the fore-limb 



