982 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of luminosity, if otherwise palatable, does not seem to escape capture. 

 An examination of the stomachs of fishes makes this clear, except 

 perhaps in the case of the herring, which, however, is chiefly a surface 

 fish. Further, it is not evident that such animals are luminous at 

 all times, for it is only under stimulation that many exhibit the 

 phenomenon. 



Moreover, the irregularity of its occurrence in animals possessing 

 the same structure and habits in every respect strengthens the view 

 just expressed. Thus, while Pliolas dactylus has been known from 

 the days of Pliny to be luminous, the common Pliolas crispnta is not 

 so endowed. Two Annelids abound between tide-marks {Harmothoe 

 imhricata and Polynoe floccosa), and closely resemble each other in 

 habits and appearance ; yet one is brightly luminous, while the other 

 shows no trace. Instead of luring animals for prey, or affording 

 facilities for being easily preyed upon, the possessors of phospho- 

 rescence in the Annelids aie often the inhabitants of tubes, or are 

 commensalistic on star-fishes. Indeed, every variety of condition 

 accompanies the presence of phosphorescence in the several groups, 

 so that the greatest care is necessary in making deductions, especially 

 if these are to have a wide application. 



" Latent period" of unstriped Muscle in Invertebrates.*— By a 

 series of experiments on a large number of animals, M. H. de Varigny 

 has shown that a very short " latent period " is not uncommon. The 

 length of the period varies (1) with the intensity of the current, (2) with 

 the mode of excitation, neural, direct, or ganglionic, (3) with the weight 

 lifted by the muscle, and (4) with a number of conditions of tempera- 

 ture, degree of fatigue, lapse of time since isolation, &c., which are 

 familiarly known to affect the length of the " latent period " of striped 

 muscle. In the more perfect unstriped muscle of the higher groups, 

 e. g. Cephalopoda, the length of the " latent period " is shorter, the 

 duration of contraction also decreases, and the number of excitations 

 required to produce tetanus is of course greater. His interesting 

 research goes to show that there are among the invertebrates un- 

 striped muscles, comparable to the unstriped muscles of vertebrate 

 intestine, stomach, lung, ureter, &c., in length of "latent period," 

 "duration of contraction," and production of tetanus; and further 

 that in Cephalopoda and Vermes there are unstriped muscles similarly 

 comparable to vertebrate striped muscle. All degrees of efficiency 

 may be observed in the invertebrate unstriped muscle from the very 

 lowest to an equality with striped muscle, so that to explain the 

 physiological differences between them, as due to their diverse histo- 

 logical structure, is inadmissible, simply because the former may 

 altogether disappear. 



Symbiosis of Worms and Sea-Anemones.t — Mr. W. A. Haswell 

 last year described a new and remarkable species of Phoronis which 

 inhabited channels in the substance of a wide tube about 6 in. long, 

 formed of felted threads, and having a smooth interior, the heads of 



* Comptea Kendus, ci. (1885) pp. 570-2. 



t Proc. Linn. Soc. N. S. Wales, ix. (1885) pp. 1019-21. 



