410 SUMMARY OF CUEEENT EESEAECHES RELATING TO 



believes that it is as yet impossible to decide between this view and the 

 suggestion that they arose separately but near together from a primitive 

 Selachian stock. 



Mechanism of Tongue in Frog.*— Prof. Marcus Hartog points out 

 that the exact method in which the tougue is everted iu the Anura has 

 not hitherto been fully explained. He finds that there is an enormous 

 lymph space between the sub-maxillary muscle and the hyoid bone. 



The petrohyoids raise the hyoid and commence its protraction, an 

 action continued by the geniohyoids. The genioglossi and hyoglossi 

 may co-operate to some extent at first, shortening the tongue and so 

 expanding its cavity ; but it is the mylohyoid which by its contraction 

 expels the lymph of the subhyoid space into the tongue, and is the true 

 " protrusor lingua? " muscle. In retraction the intrinsic muscles pull 

 the tip of the tongue backwards, and the median portion of the genio- 

 glossi especially pull its base downwards and inwards. The sterno- 

 hyoids and omohyoids retract the body of the hyoid bone, with its 

 attachments to the tongue, and the closure of the mouth by the levators 

 of the mandible presses the tongue against the roof of the mouth, and 

 so expels the lymph from its cavity. Clearly this sudden propulsion 

 of the tongue of the Anura is an erection, and is thus comparable with 

 the sluggish protrusion of the foot in Lainellibranchs, also too often 

 miscalled a " protraction." 



Tunicata. 



Histology of Ascidians.j — P. Vignon finds that the ciliated cells 

 of the branchial sac in Ascidians confirm his view that the basilar 

 granulations of the cilia have nothing to do with the motion of the 

 cilia. Such granulations represent the most frequent method of in- 

 sertion of the cilia, but not the only possible one. He also discusses 

 the mechanism of secretion of the " liver " cells in Ascidians. 



Development of Branchial Sac in Corella4 — Marc de Selys Long- 

 champs finds that in Corella parallelogramma there are six pairs of pro- 

 tostigmata, but these in all probability arise from primitive slits. Each 

 of these six divides first into two, then into four, and these later take 

 on a crescent shape. The crescents divide, and later form spirals. The 

 author contrasts in detail this method of origin with that found in Ciona,. 

 Ascidiella, and Molgula. 



INVERTEBRATA. 



Plankton of West Coast of Norway.§ — E. Jorgensen has studied 

 the seasonal variations in the surface flora and fauna in the vicinity of 

 Bergen. From January to March organisms are few both as regards 

 individuals and species. About the end of March great numbers of 

 Diatoms suddenly make their appearance, and persist for a few weeks, 

 to be then as suddenly replaced by PeridinieaB and Rotatoria. These 



* Comptes Rendus, exxxii. (1901) pp. 388-9 ; Ann. and Mag. Nat. Hist., vii. 

 (1901) pp. 501-3. t Tom. cit., pp. 714-6. 



X Arch. Biol., xvii. (1900, published 1901) pp. 673-711 (1 pi.). 



§ Bergena Museums Aarbog, 1899 (published 1900) pp. 1-112 (4 pis.). See also 

 Bot. Centralbl., lxxxv. (1901) pp. 66-8. 



