64 ADAM SEDGWICK. 



dseum, so that one may be regarded as a mouth aud the other 

 as an anus. 



I have not been able to make out what causes the adhesion 

 of the lips of the siphonoglyphe in Peachia (whether inter- 

 locking of cilia as in Lamellibranch gill or what)^ but of the 

 adhesion there can be no doubt whatever. 



This differentiation of the mouth and stomodseum of 

 Actinozooid polyps has been known for some time. The 

 Hertwigs/ in their brilliant paper on the Actinozoa^ sum- 

 marise the facts and point out that the elongated mouth when 

 closed has a dumb-bell shaped form, the median portion being 

 closed, and the two ends remaining open. 



" Wenn die Wandungen des Schlundrohrs an einander legt 

 siud und der Mund geschlossen ist, bleiben sie (the ' Schlund- 

 rinnen ') geoffiiet und wird demnach ihre Bedeutung wohl 

 darin bestehen, dass durch sie fortwahrend ein Wasserstrom in 

 das innere des Korpers hinein getrieben wird " (p. 513). 



In view of the hypothesis under consideration, viz. that the 

 mouth and anus of the higher animals is derived from an 

 elongated slit-like opening such as is found in the Actinozoa, 

 these anatomical facts are of the highest interest. 



Blastopore of Peripatus. — The history of the blastopore of 

 Peripatus has been given up to a certain point in the last 

 volume (1883) of this Journal.'^ The youngest embryo found 

 was a spherical or slightly oval gastrula with a slightly 

 elongated blastopore (fig. 1). In the subsequent growth the 

 embryo becomes elongated along the long axis of the blasto- 

 pore and the mesoblastic somites appear (fig. 2). The middle 

 portion of the lips of the blastopore then come together (fig. 3), 

 and in the next stage (fig. 4) there are two openings into the 

 mesenteron, an anterior and a posterior. Meanwhile, the 

 primitive streak (connected with the formation of the meso- 



' "Die Actinien," 'Jena Zeitschrift,' vol. xiii, p. 513. 



- The species of Peripatus which Dr. v. Kennel is working at is different from 

 that described in Balfour's memoir. Dr. v. Kennel does not mention this 

 somewhat pertinent fact. Perhaps he was not aware of it ; but if he was, I 

 find it difficult to understand the positive nature of his criticism. 



