764 RECORD OF CURRENT RESEARCHES RELATING TO 



(12) The " rectal plug " changes its position from the centre of the 

 shell-area to a point on the ventral surface, where it forms the 

 definitive anus. 



(13) The structure and history of the shell-area is substantially as 

 described by Eay Lankester. 



(14) Periods of rest very conspicuously alternate with periods of 

 segmentation. 



The above observations apply to the Pulmonata, and the history 

 of the same parts in the oyster is not altogether the same ; in both 

 cases, however, the blastopore is converted into the shell-area, and 

 the mouth is formed nearly opposite, by an invagination of the ecto- 

 derm. The anus is in both distinct from the blastopore, but the in- 

 testine of the oyster appears to have no relation to the " invagination 

 neck." 



Further details are promised, and will be welcomed, as the 

 subject is one on which very various statements have been made 

 by those embryologists who have directed their attention to this 

 phylum. 



Action of Poisons on the Cephalopoda.*— M. Yung gives an 

 account of the effect of certain poisons on the Dibranchiate forms on 

 which he has been enabled to experiment : — 



Curare when injected subcutaneously has no action, but if two or 

 three drops were injected into the cephalic artery they almost instan- 

 taneously brought about a paralysis of the muscles of the mantle, and 

 then of those of the arms ; although the animal then appeared to be 

 dead, the " hearts " continued to beat, and the chromatophores retained 

 their activity. 



Stryclinine has a very powerful influence, for 1 part in 30,000 of 

 sea-water produced a relaxation of the muscles of the chromatophore ; 

 the respiratory movements increased and then fell rapidly ; tetanus 

 shortly followed. The animal emptied its ink-bag, and a state of 

 extreme muscular rigidity was induced ; examination nevertlieless 

 revealed the fact that the venous hearts were still beating. 



Nicotine is still more poisonous to the Cejihalopod, but it produces 

 a contraction of the muscles of the chromatophores, and the hearts 

 were arrested in their systole. 



Atropine appears to have a very complex action, large quantities 

 are necessary to produce any effects, and these consist in the gradual 

 lowering of the cardiac and respiratory movements. 



Verairin is an active poison, and produces ii-regularity of move- 

 ment, and an arrest in systole of the hearts. 



Muscarin has a similar action to nicotine on the chromatophores, 

 but the effect is not so well marked ; it would appear to slowen the 

 circulation and to increase the secretions. 



Upas antiar, when injected into the cephalic artery, has the effect 

 of throwing the animal into violent couvulsious, the cardiac move- 

 ments become very irregular, and after a period of acceleration come 

 to an end in the period of systole. 



* ' Comptes Keudus,' xci. (1880) p. 306. 



