416 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



branclis seem, in many cases, to have wide areas of distribution and 

 to be found also at very different depths ; as a rule, very deep forms 

 tend to be colourless and of thin structure ; on the whole, MoUusca 

 seem to be comparatively scarce at great depths. 



MoUuscoida. 

 a. Tunicata. 



Alternation in the Heart of Tunicates.* — M. F. Lahille gives 

 the results of numerous experiments on the reversal of the action 

 of the heart in Salpa maxima and Phallusia mamillata. 



The number of beats in each direction is not regular, but it is 

 found that the number of " cardio- visceral " beats is greater than that of 

 " cardio-brancliial " beats, before a reversal takes place : he gives tables 

 showing these numbers under various circumstances. Immediately 

 after its capture, the beats varied from 4 cardio-visceral and 2 cardio- 

 branchial, to 9 and 7 respectively. As the length of captivity 

 increased, the number of pulsations before a reversal took place 

 increased ; but still the cardio-visceral beats were in excess : for 

 instance, 26 beats before a reversal ; then 12 cardio-branchial beats ; 

 or even 60 and 48. Under the influence of a current of oxygen, the 

 number of pulsations decreased, and tended to become normal : with 

 carbonic acid, the inverse result was obtained : the number of pulsa- 

 tions increases, and the cardio-branchial exceed the cardio-visceral 

 pulsations, e. g. 60 and 52 between reversals. The same thing 

 happens as the captivity is prolonged ; from which he concludes that 

 the difficulty in keeping Salpse alive in aquaria arises from their great 

 need of oxygen. The pulsations, either visceral or branchial, occur once 

 in every 2^ seconds, either normally, or with oxygen, or with carbonic 

 acid. 



With Phallusia mamillata the same general results were obtained ; 

 but the number of pulsations between reversals is greater, and more 

 irregular ; sometimes the cardio-visceral pulsations exceeding the 

 branchial ; sometimes the reverse is the case. The time between 

 each contraction varies from 9 to 11 seconds. Carbonic acid does 

 not seem to influence the number of pulsations, but the intervals 

 between contractions are longer. The removal of the intersiphonal 

 ganglion sometimes increases, sometimes diminishes, and at other 

 times does not affect the number of pulsations ; but in all cases it 

 appears that the passage of blood to the branchia is more difficult 

 than towards the viscera ; the blood seems to flow back slightly 

 from the branchia. The author intends to explain these results in 

 a future paper, and to try the action of alkaloids and anaesthetics, &c., 

 on these forms and on the Synascidise. 



Budding of Salpae.t — Herr 0. Seeliger, after an historical review 

 of what is known with regard to the budding of Salpos, gives a 

 detailed account of the formation of the stole prolifer. 



* Bull. Soc. Hist. Nat. Toulouse, xix. (18S5) pp. 13-23. 



t Juuaisuh. Zoitscbr. f. Naturwiss., xix. (1885) pp. 573-677 (10 pis.). 



