534 KNOWER. [Vol. XVI. 



Oecanthus, Gryllus, or the Termite. These forms should be 

 looked to for a connecting link, if one exists (on this question 

 refer to the discussion of the origin of the amnion in insects in 

 the last division of this paper), between the phenomenon of 

 "doubling-up," exhibited by the myriopod embryo, and the 

 formation of an amnion in the Pterygota. 



There is much reason for believing the development of 

 the Libellulid to be secondary, since the embryo is of the "im- 

 mersed " type. 



A. A superficial germ-band is generally characteristic of 

 Arthropods, and when we find one sunken into the yolk, there 

 is cause to believe this position has been assumed secondarily. 

 Among the insects, most forms (and especially the Orthoptera 

 and Termites) agree in having superficial embryos. The excep- 

 tions are rather marked, and are found among the Lepidoptera, 

 Hemiptera, and Libellulids. In the Lepidoptera, as in the 

 Myriopoda, the "immersed" position is admitted to have been 

 secondarily derived from the superficial for protection, nutri- 

 tion, or some other unknown cause. It appears to me most 

 probable that the same is true for the Libellulids and the 

 Hemiptera, with inner germ-bands. 



Hence I should regard the superficial embryos of the Orthoptera 

 and the Tertnite as more typically primitive for insects. 



B. A striking character of the development of the Termite 

 is the small size of the first rudiment of the embryo, the germ- 

 disc, when compared with the definitive length of the embryonic 

 band. The primary rudiment must elongate through the whole 

 length of the egg, and add successively all the segments of the 

 body before the embryo is fully formed. This is equally notice- 

 able in the case of some of the Orthoptera, but is less pronounced 

 in most insects, particularly among the more specialized forms 

 of the group. In these there is a tendency toward a formation 

 of the embryonic band in its full extent from the start. 



Now it seems to me that the Termite and the Orthoptera, with 

 a superficial embryo beginning in a disc which must elongate 

 considerably to attain the definitive number of segments, have 

 adJicrcd most nearly to the typical method of development for 

 Arthropods, and probably best represent the embryonic develop- 



