42 Mr. R. Valleiitin on (he 



P. II. Gosse (0) followed Prof. William.son with a short 

 paper on the same Rotifer in the same number of the same 

 journal. A few years later he (Mr. Gosse (7)) published an 

 elaborate treatise, furnished with numerous illustrations of the 

 niastax, with the contained hard parts, in various species of 

 Rotifers, this last work having since then formed the standard 

 work of reference in connexion with this organ. In this 

 last-named work Mr. Gosse, after giving a short summary of 

 Prof. Williamson's investigations in connexion with the 

 structure of the mastax, concludes as follows: — "He [Prof. 

 Williamson] further states, that ' the conglobate organ in 

 which the apparatus is imbedded [/. e. the mastax] is com- 

 posed of numerous large cells, eacli of which contains a 

 beautiful nucleus with its nucleolus.' . . . The statement of 

 the cellular character of the mastax, and the presumption of 

 penetrating muscles, are alike negatived by my observations, 

 not only in this species, but in the whole range of the Roti- 

 fera. The able and learned Professor has probably been 

 misled, in the former conclusion, by some overlying tissues, 

 perhaps similar to the salivary glands in Euchlanisy With 

 reference to the mastax, taken as a whole, Mr. Gosse says : 

 " In substance it varies from a state in which its walls arc 

 thick and solid, composed of dense muscular fibre, with little 

 cavity, as in DracMonuSj to one in which it forms a capacious 

 sac, with thin, apparently membranous, parietes, as in Fur- 

 cularia. ... In Brachionus iirceolaris it (the mastax) is a 

 dense, colourless, highly refractive mass of muscles. . . ." 



Dr. Hudson makes remarks of a similar nature in his 

 description of Brachionus ruhens. He says : " Muscles, 

 springing from the walls of the mastax, are attached to various 

 parts of the mallei and rami, and act so as to cause the unci 

 to approach and recede from each other." 



A carelul examination of serial sections taken through the 

 mastax and the surrounding parts of Brachionus ruhens^ 

 Melicerta ringenSj M. conifcra, and Lacinularia socialis has 

 failed to reveal to me the slightest trace of the muscular 

 investment described and figured by Mr. Gosse and other 

 investigators. 



Considering the crude methods employed by Prof. William- 

 son when he made his important discovery of the cellular 

 character of the mastax, one can readily excuse the position in 

 which he imagined these cells to be placed, for sections show 

 these cells to be placed within the hard parts of the tropin, and 

 not on the walls of the mastax. I have placed in my illustra- 

 tions an almost comj)lcte series of drawings of sections taken 

 through the anterior tliivd of Mtficcrfa coniflra, I have 



