KEPORT ON THE GREEN TURTLE. 3 



The oral space {in.) is a narrow slit from side to side, the fore-brain being bent very 

 near to the mandibular fold {mn.), which is twice as large as the others, and lies almost 

 horizontally. In front of this, in the sub-orbital region, a very slight rudiment of the 

 maxillo-palatine fold {mx.p.) is seen, but the naso-frontal fold is not yet formed. 



Second Stage. Embryo, 6 lines (^ inch) long. — In this stage (PL I. fig. 2) the embryo has 

 added a large number of somatomes, there being almost twice as many as in the last stage. 



The heart has now its three compartments tolerably distinct. The cephalic flexure 

 is the same as in the last stage, as is also the outer fonn of the head with its cerebral 

 enlargements. 



The rudiments of the nose, eyes, and ears {ol.,e.,au.) are more definite, and the 

 openings of the latter are still quite evident. The pituitary involution is beginning, and 

 the oral space [m.) is wider ; the four long arcuate clefts [cl. 1-4) are narrow, but clearly 

 open slits, with a definite margin, and are enclosed by five visceral folds, the mandibular 

 (inn.), the hyoid iliy.), and three corresponding to branchial folds. 



The maxillo-palatine fold (^mx.p.) is now in the form of an oval leaf, broad against 

 the mandible, and with a sharp point towards the nose ; between its anterior margin and 

 the eyeball (e) there is a very definite hollow space, the lachrymal cleft {l.cl.), which, like 

 the continuous oral clefts, appears to be homologous with those behind the mouth. The 

 naso-frontal folds are still not apparent. 



Third Stage. Embryo of Green Turtle, length along the axis 6^ lines. — In this stage 

 the embryo is fairly formed, for there are rudiments of all the principal organs. 



The somatomes were apparently all marked out, for I could count fifty-two at least 

 behind the head (PI. I. fig. 3) ; the segments of that part are more obscurely indicated, 

 but by counting the " clefts " — four post-oral, two pre-oral, and one oral^it is evident 

 that there are, at least, seven. 



Hence we may conclude that the primitive form of this type was composed of not 

 less than sixty segments, or about half as many as are seen in the lesser and shorter 

 kinds of serpents, and considerably less (about 5-6ths) than are present in the embryo 

 of a swan.' 



Three folds had separated the embryo from the yolk — the head-fold, the tail-fold, 

 and the side or body-fold. The two former had made the embryo lie free at its 

 extremities, and altogether the three parts of the general enfolding had given to it a 

 great distinctness from the nourishing mass below. 



The head, as well as the tail, is seen to have curled itself round towards the sup- 

 porting and sustaining yolk, hence the mesocephcdic flexure, which results in most 

 important modifications in the organs and parts of the cephalic region. 



' In working out this type I shall proceed on the supposition that the head is a segmented region as well as the 

 body, and make it part of my business to show and interpret the signs of the archaic segments. 



