170 NEURENTElilC CANAL. 



It will be. convenient at this point to say a few words as to what 

 is known of the further fate of the neui-eiiteric canal, and tlie early develop- 

 ment of the allantois. According to Strahl, who has worked on Lacerta 

 vivipara, the canal gradually closes from below upwards, and is obliterated 

 before the completion of the neural canal. The hind end of the alimentary 

 tract appears also to become a closed canal before this stage. 



In Lacerta muralis the history appears to be somewhat different, and 

 it is more especially to be noticed that in this species the hindgut 

 does not become closed till considerably after the completion of the neural 

 canal. In a stage shortly after that last described, the ueurenteric passage 

 becomes narrower. The next stage which I have observed is considerably 

 later. The neural canal has become completely closed, and the Hexure of 

 the embryo has already made its appearance. There is still a well -deve- 

 loped, though somewhat slit-like, neurenteric passage, but from the analogy 

 of birds, it is not impossible that it may have in the meantime closed up 

 and opened again. It has, in any case, the same i*elations as in the previous 

 stage. 



It leads from the end of the medullary canal (at the point where its 

 walls are continuous with the cells of the primitive streak) round the end 

 of the notochord, which here becomes continuous with the medullary cord, 

 and so through the hypoblast. The latter layer is still a flat sheet without 

 any lateral infolding ; but it gives rise, behind the neurenteric passage, to 

 a blind posteriorly directed diverticulum, placed in the body cavity behind 

 the embryo, and opening at the ventral face of the apparent hind end 

 of the primitive streak. There is very little doubt that this diverticulum 

 is the commencing allantois. 



At a somewhat later stage the arrangement of these parts has under- 

 gone some changes. Their relations are shewn in the sections represented 

 in fig. 128. 



The foremost section (A) passes through the alimentary opening of the 

 neurenteric passage (ne). Above this opening the section passes through 

 the primitive streak {ipr) close to its junction with the walls of the 

 medullary canal. The hypoblast is folded in laterally, but the gut is still 

 open below. The amnion is completely established. In the next section 

 figured (B), the fovirth of my series, the gut is completely closed in; and the 

 mesoblast has united laterally with the axial tissue of the primitive streak. 

 Vessels to supply the allantois are shewn at v. 



The three following sections are not figured, but they present the same 

 features as B, except that the primitive streak gets rapidly smaller, and the 

 lumen of the gut narrower. The section following (C) represents, I believe, 

 only the stalk of the allantoic diverticulum. This diverticulum appears 



the early Lacertilian development, more especially in what concerns the so-called 

 neurenteric passage. They believe this structure to be closed below, and to form 

 therefore a blind sack open externally. The open end of this sack they regard as the 

 blastopore — an interpretation which accords with my. own, but they regard the sack as 

 the rudiment of the allantois, and hold that it is equivalent to the invaginated archen- 

 teron of Amphioxus. I need scarcely say that I believe Kupffer and Beuecke to have 

 made a mistake in denying the existence of the ventral opening of this organ. Kupffer 

 in a subsequent paper (No. 155) states that my descriptions of the structure of this 

 organ do not correspond with the fact. I have perfect confidence in leaving the decision 

 of this point to future observers, and may say that my observations have already been 

 fully confirmed by Strahl (No. 160), who has also added some observations on the later 

 stages to which I shall hereafter have occasion to allude. 



