I40 WHITMAN. [Vol. I. 



own observations, it will be well to consider briefly some points 

 respecting the germ-bands. 



Use of the Term Germ-bands. — It is important to settle 

 at the outset precisely what is to be understood by the term 

 " germ-bands." Keimstreifen, the German equivalent, is usually 

 restricted to the strata derived from the teloblasts, the epider- 

 mal layer being excluded. It is, furthermore, generally believed 

 that the germ-bands of the annelids embrace only mesoblastic 

 elements. Although appearances may often favor such a re- 

 stricted use of the term, we cannot so limit it in all cases. The 

 idea that the germ-bands are purely mesoblastic has already 

 led to much confusion. In the Hirudinea it is perfectly certain 

 that ectoblastic elements must be included, and hence the mat- 

 ter is not in the least simplified by excluding the epidermal 

 stratum. In Lumbricus, where, according to Wilson, the neuro- 

 blasts and nephroblasts are at first ordinary ectoblastic cells, 

 and where, after sinking beneath the surface, they remain im- 

 bedded in the epidermal layer, it is obvious that this layer can- 

 not well be held to be distinct from the elements of the germ- 

 bands. According to Bergh (No. 9) the " definitive epidermis " 

 in the Gnathobdellidae arises from what I shall call the neiiro- 

 nephric stratum of the germ-bands. I cannot, therefore, fol- 

 low Kowalevsky, Biitschli, Hatschek, Balfour, Goette, and 

 numerous other writers in the use of " mesoblastic bands " as 

 the equivalent of germ-bands, nor can I accept the alternative 

 offered by Bergh (No. 9, p. 285), which denies the homology 

 of the germ-bands. The moment we undertake to exclude 

 ectodermic elements, the basis for homology is sacrificed, and 

 the door is open to endless confusion. I shall, therefore, include 

 in the term germ-bands both the " mesoblastic bands " and the 

 superjacent ectodermic strata. It must be remembered, also, 

 that the term, as here used, has reference only to the body of 

 the embryo. 



Germ-bands of the Head. — The relations of the cephalic 

 lobe to the germ-bands have not yet been made clear in Clep- 

 sine. In Aulostoma, Bergh (No. 9) finds in the head two dis- 

 tinct germ-bands, which arise independently of each other and 

 of the germ-bands of the body. The head-bands (" Kopf- 

 keime") contain epidermal, neural, and muscular elements, and 

 are regarded as homodynamous with the trunk-bands (" Rumpf- 



