366 A. A. W. lIUBRECriT. 



In Nemertines these diverticula become constricted off from 

 their point of origin — the oesophagus — and entering into con- 

 nection with invaginations from the epiblast, which bring 

 about a free access of the external sea-water, they become 

 converted — at least in the large section of the Schizonemertines 

 — into an apparatus which I have proved to be subservient 

 ('ZurAnatomie u. Physiologie der Nemertinen/ p. 28) to a 

 process of cerebral respiration, in which oxygen is carried to 

 the nervous system itself, the cellular elements of which are 

 in this subdivision profusely provided with hsemoglobin. 



I am not prepared to say that in the great subdivision of 

 the Hoplonemertini, where the central nervous apparatus is no 

 longer provided with hsemoglobin, but where, on the contrary, 

 the circulating fluid is, these diverticula, which continue to de- 

 velop in the same way out of the oesophagus, are also — and in the 

 first place — subservient to a respiratory process. I am rather in- 

 clined to believe that in this group the cephalic grooves — as the 

 epiblastic invaginations travelling inwards to meet the hypo- 

 blastic diverticula in question are called — remain more especially 

 adapted for sensiferous purposes, probably of olfactory nature. 

 The way in which the complicated organs in the adult, the so- 

 called side organs, develop, remains quite the same : an out- 

 growth from the oesophagus coalesces with an ingrowth from the 

 epiblast, the principal difference being that the connection with 

 the brain-lobes is no more so intimate, and that the apparatus is 

 connected with the brain by a special set of nerves. In some 

 species it continues to be situated behind the brain, in others 

 it becomes placed in front of the central nervous apparatus. 



It appears to me that these facts are not without significance. 

 However, I refrain for the present from a further discussion, 

 and would merely wish to point to an interesting detail in the 

 development of Amphioxus lately brought to light by Ilatschek's 

 researches. It is the presence in the anterior region of the 

 oesophagus, in front of the mouth, of two lateral hy po- 

 blastic diverticula, differing in their nature and in their 

 further development, both from the archenteric diverticula 

 (mesoblastic somites), and from the branchial outgrowths of 



