MOKPHOLOGY OF CYCLOSTOMATA. 329 



From this part backwards it gradually decreases in width 

 until no space is perceptible. Anteriorly the cavity is also some- 

 what narrowed, Init not as much as in its posterior contin- 

 uation, aud ends blindly rather suddenly at its anterior end 

 (hg. 32). The anterior portion of the Anlage forms a blunt conical 

 tube (Fig. 32, a.pn.l) projecting anteriorly and lying between the 

 dorsal edge of the lateral plate {Im.) and the lower surface of 

 the fourth myotome {mt.IV). The existence of this conical 

 tube^' gives us a strong impression that originally there must have 

 been present an Anlage of the pronephros in the anterior segment 

 which was connected by a connecting cord with the Anlage 

 belonging to the fourth somite, but had disappeared during the 

 phytogeny and that this conical tube is the remnant of this 

 connecting cord.-' 



The next posterior Anlage, which is found under the liftli 

 myotome (%s. 37-30, a.pn.2) and shows an outline much re- 

 sembling that represented in tigs. 32-35, has an internal cavity 

 of irregularly triangular form, extending through three sec- 

 tions, of which the foremost section contains the most spacious 

 cavit}^, while in tbe others the lumen grows smaller and smaller. 

 The pronephric Anlage in the next following somite (tigs. 41-43, 

 a.pn.3) has an outline much like that shown on the left side of 

 Figs. 18 and 24, being in the same phase of development, that is, 

 it is of the form of an isosceles triangle whose two basal angles 

 touch the myotomes. This Anlage is found under the sixth 



1) Tlie internal cavity of this conical tube is not entirely closed, but there is clearly seen 

 a small canal {%) directed towards tlie median side and opening below the myotome. I can 

 not decide, at present, -whether this canal is normal or abnormal ; for I cau not make out the 

 corresponding structure on the opposite side and have no other embryo of exactly the same 

 stage, in which the structure in question would probably be found, if it be of some definite 

 meaning ; I also can not detect any trace of such a canal in eml)ryo.s of advanced or younger 

 stages. 



2) See the descrijition under I'eriod. 1. 



