412 GEITEEAL HISTOET OF THE INFFSOEIA. 



to be vesicular, and not improbably salivary glands (XXXVIII. 27 I). Mr. 

 Huxley alludes to these structiu'es in the ensuing account : — " On each side 

 the pharynx is a yellowish horny-looking mass, which sometimes appears 

 cordate, at others, more or less completely composed of two lobes. I believe 

 its function is to give strength to the deUcate walls of the pharynx, and that 

 it is, therefore, to be considered a part of the horny skeleton." 



The pharynx ends mostly below, and partially embraces the " maxillary 

 bulb " or "mastax,^^ which contains the maxillae or jaws supporting the ''teeth," 

 and has its mass made up of nuclear cells and muscular fibres (XXXYIII. 

 2Q m). In the living animal the bulb is almost constantly in motion, con- 

 tracting and expanding itself in what some have called a " peristaltic " manner. 

 This alternate and constant movement, visible even in the embryo before escap- 

 ing from the eg^, was mistaken by Bory St. Vincent, and other of the older 

 microscopists, for the pulsating action of a heart. The apparatus, however, 

 is rather comparable to the gizzard of birds, or to the tooth -crushing 

 mechanism in the stomach of lobsters and other Crustacea, though not, 

 indeed, homologous with it. The '' maxillary bulb " is bulky, more or less 

 globose, with a prevailing tendency to a triangular figure "sv'ith rounded 

 angles (XL. 20, 23, 24). Sometimes it is oval or ovoid, and still more com- 

 monly heart-shaped, from being notched or furrowed on one side, indicating 

 a bilobed structure. In Melicerta Mr. Gosse figures and describes a third 

 lobe, below the usual "two globose bodies (or rather the bilobed single 

 mass), equally hyaline and probably muscular, which seems united to the 

 two others, and alters in form as they and the jaws work, lengthening down- 

 ward as they approach, and dilating and shortening as they recede " 

 (XXXVII. 23). 



The mass of the " maxillary bulb " surrounding the maxillse has been 

 generally assumed to be muscular, and, as such, actively concerned in work- 

 ing the contained jaws. Gosse calls it a " muscular sac," and has even 

 attempted the description of its component miLscular bands. Leydig has re- 

 presented the jaws to be acted on by exquisitely striated muscles (XXVII. 

 31). Prof. Williamson admits the existence of muscles affixed to the pro- 

 cesses of the jaws, but states that the conglobate organ in which these are 

 imbedded " is transparent, and composed of numerous large cells, each of 

 which contains a beautiful nucleus with its nucleolus. The cells are only 

 seen when the organ is ruptui'ed between two plates of glass, when they 

 readily separate from one other ; but the nuclei, with their contained nucleoU, 

 are distinctly visible in the living animal. Delicate muscular thi^eads 

 most probably penetrate tliis organ to reach the dental apparatus, though I 

 have not yet detected them." Here a great discrepancy of opinion appears, 

 between Mr. "Williamson and Leydig and most other writers, respecting the 

 constitution of the globose mass of the maxillary bulb, and such as only 

 reiterated examination can remove. 



Dr. Leydig asserts that the bulb is covered externally by a chitinous 

 membrane, of the same nature as the cuticle, and that the existence of a like 

 membrane in its interior, developed for a special end, constitutes the maxillae 

 and appendages, just as bristles and homy plates and processes are developed 

 out of the external cuticle. 



The maxillary apparatus, contained within the soft mass of the bulb, is 

 visible without any preparation, but may, from its hardness, be detached by 

 strongly compressing or crushing the animal. Although much denser than 

 the soft tissues of the body, yet like them the dental apparatus disappears 

 by decomposition. Ehrenberg having an enormous number of Brachioni 

 in a vessel of water, evaporated the fluid, and ha^ing burnt the desiccated 



