Miscellaneous. 277 



memoir on this subject, that of L. Fredericq *, on the muscles of 

 the lantern of Ecldnus spJicera, their striation is again denied. How 

 are we to explain this utter confusion ? 



By treating the muscles of the Urchin with different reagents 

 and making a considerable number of preparations we have seen all 

 the phenomena described by these authors. Frequently the adduc- 

 tor muscles of the valves of the pedicellarise are distinctly striped ; 

 frequently also they do not show the least trace of striation. The 

 same fact may be observed with the muscles of the lantern ; for we 

 have preparations which contain the simple fibres of "Wagner and 

 Fredericq side by side with others of which the striation is as evi- 

 dent as in Valentin's drawings. Moreover by passing along a 

 single fibre we very frequently find all possible gradations between 

 the most distinct striation and its complete absence. 



Our colleague, Mr. Haycraft, has just proposed a new theory upon 

 the structure of the voluntary muscles f. In his view the fibrils are 

 not simple cylinders, but they are slightly constricted at small 

 intervals ; and he asserts that their striation does not indicate a 

 histological differentiation, but is simply an optical phenomenon 

 produced by the unequal refraction that the light undergoes in 

 traversing the fibril. 



Without wishing to pronounce an opinion upon this theory from 

 a general point of view, and without afiirming that the striation of 

 the muscles of the Echinodermata is due to the same cause as that 

 of the muscles of the higher animals, we are convinced that the 

 irregularity of the striation in the Echinus may be explained in the 

 same way. 



The fibres of the lantern show constrictions in perfect correspon- 

 dence with the transverse strise ; when these constrictions follow one 

 another very rapidly the striae also approach each other ; and when 

 they become more widely separated the strise show the same irregu- 

 larity. Lastly the strise and the constrictions disappear together. 



It is probable, as has already been suspected, that the striation 

 stands in some relation to the state of contraction of the muscles ; 

 but we hope to make fresh observations before pronouncing an opinion 

 upon this question. — Gomptes Renclas, February 7, 1881, p. 308. 



Oh the Formation of the Blastoderm in the Araneida. 

 By M. A . Sabatier. 



The mode of formation of the blastoderm in the Araneida has 

 given rise only to a small number of publications, the data and 

 conclusions of which are contradictory. The phenomenon presents 

 two distinct phases : the first terminates in converting the egg into 

 a meroblastic ovum with multiple cicatriculai ; the second includes 

 the discoidal segmentation of each of the cicatriculae, so as to form 

 a simple and continuous layer of blastodermic ceUs. 



* Arch, de Zool. Exp(^r. 1877. 



t Proc. Royal Soc, February 1881. 



