20 SUMMARY or CUERENT RESEARCHES RELATING TO 



Secondary Muscle-wave.* — M. C. Eichet describes the phenomena 

 associated with the fact that after each muscular contraction the fibres 

 are in such a condition that they can, without any fresh stimulus, 

 contract a second time. This phenomenon is masked by the fact that, 

 the muscle being then very feeble, slight weights are sufficient to 

 prevent its being apparent. 



If we take a very fresh muscle of a crayfish and attach to it a 

 slight weight (say 4 grammes), and stimulate it for one or two seconds 

 by a repetition of strong induction currents, the muscle relaxes as 

 soon as the stimulus ceases ; but, a few seconds afterwards, it con- 

 tracts afresh, and returns more or less to its tetanic condition. This 

 second contraction is eflected by successive rhythmical waves, but it 

 is not to be demonstrated if the stimulation is feeble, or if the muscle 

 is weak, or if the weight is too great ; in no case was the secondary 

 wave seen when the weight attached was greater than 10 grammes. 

 The author, however, thinks it probable that there is such a wave 

 even in cases where it is impossible to demonstrate it, and he is of 

 opinion that to its existence we owe the remarkable phenomenon of a 

 number of apparently inefficacious stimuli finally making the muscle 

 much more sensitive to such effects. 



B. INVERTEBRATA. 



Marine Organisms in Captivity. t — Some interesting particulars 

 as to the habits of various marine animals and plants are given by 

 Herr R. Schmidtleiu, of the Zoological Station at Naples. 



Among animals breeding in the aquarium, none are so easily 

 observed as the larger crustaceans and molluscs, which pair repeat- 

 edly and lay great clusters of eggs. Two species of Maia (squinado 

 and verrucosa), pairing from January to July, are good examples of 

 their class. Copulation is most frequent in spring. After many 

 fruitless attempts, the long, awkward legs of each apposed couple 

 duly adjust themselves, and the two animals become firmly inter- 

 locked, their sterna being mutually approximated, while the post- 

 abdomen of one is closely pushed against that of the other. The male 

 is underneath ; with his huge chelaa he clutches the orbital margins of 

 his consort. The process may last over an hour, and when completed 

 the female resumes her usual position ; the male sits upon her, 

 and defends her with his nippers against rival gallants. Zocese of 

 these crabs could not, however, be bred, though swarms of Phyllosoma 

 were got from Palinurus in the same tank. Lobsters, notwithstand- 

 ing their salacity, rarely produced eggs in captivity. 



Of Mollusca, the best breeders are species of Loligo, Sepia, Aplysia, 

 and Doris. Loligo lays its eggs, a few days after being captured, on 

 Posidonia and rocks. The males of Sepia, when sexually most active, 

 display very brilliant colours. Aplysia surpasses all other inhabitants 

 of the aquarium in its abundant oviposition ; during brief intervals 

 from the work of reproduction, these animals devoured with 



* Comptes Kendus, xci. (1880) pp. 828-9. 



t MT. Zool. Stat. Neapel, ii. (1880) pp. 162-75. 



