148 PANTOPODA. 



the region beneath which the mesoderm extends may be regarded as 

 the germ-band, the Pantopoda, as has already been pointed out, 

 agreeing in this respect with other Arthropods. 



Should the appearance of primitive segments and their extension into the 

 limbs be confirmed, a strong resemblance to the Arachnida would be established. 

 Peripatus, indeed, and many of the Insecta, show the same arrangement, but 

 we do not feel confident in laying so much stress either on this or on the 

 similarity to the ventral organ which Morgan specially points out. Trans- 

 verse sections of embryos of Pallene (Morgan) and of Nymphon (Hoek) show 

 unmistakable similarity to sections of a spider. 



The further development of the mesoderm, its relation to the 

 adult body-cavity, and the formation of the heart, have not yet been 

 ascertained with stifficient certainty. The heart appears in the dorsal 

 middle line after the mesoderm has already given rise to a number 

 of schizocoele-like cavities. More accurate accounts of the participa- 

 tion of the primitive segments in these processes (the further 

 differentiation of the mesoderm and the formation of the heart) 

 would be of great interest. 



The mesodermal tissue with its cavities increases in extent as the 

 yolk-mass degenerates. The latter is absorbed by the surrounding 

 entodermal epithelium. Yolk-cells do not appear to play any 

 special part in this process, and may, indeed, be wanting. The 

 enteron becomes connected with the stomodaeum, which is derived 

 by Morgan from the invagination already mentioned as appearing 

 very early. The proctodaeum does not appear until very late, when 

 the seventh pair of limbs and the abdomen form. 



The Form of the Larva and its Transformation into 



the Adult. 



The Larva. Most of the Pantopoda develop through metamor- 

 phosis. The larvae usually have three pairs of limbs, but some 

 leave the egg in a more advanced condition ; the young Pallene y 

 for instance, when hatched is provided with all the limbs of the 

 adult, and this higher stage of development is also attained in the 

 egg by a few species of the genus Nymphon. The various species 

 of this genus differ from each other in this point ; in some of 

 them the larva, at hatching, has only four or five pairs of limbs 

 (Hoek). 



The many Pantopodan larvae that have been described differ only 

 slightly from each other, and are easily derived from a larval form 

 provided with three pairs of limbs. This form, which was first 



