LOXOSOMA. 359 



towards the anterior extremity of the boflj, and the hood is thus 

 turned downwards towards the ventral aspect, of which it occupies 

 the upper half. When it is fully extended, if the polypide is 

 viewed in profile, a membranous expansion is visible, distinctly 

 separated from the wall of the body by a circular depression, 

 having the form of a crown, slightly raised and delicately crenated 

 round its outer edge. When, on the contrary, the hood is con- 

 tracted, it completely conceals the tentacles folded in towards the 

 interior, and its orifice is reduced to a circular spot, which it is 

 often difiicult to detect. The cavity, enclosed in front by the 

 hood and below by the internal organs, is the vestihule (c, 

 PI. XXII, fig. 1). 



The hood is eminently contractile, its contractibility being due 

 to a large circular sj^hincter {e), composed of delicate, parallel 

 muscular fibres, which form a band round its orifice. 



Radiating muscular fibres to act as antagonists the Author has 

 failed to find, nor has he observed any histological element 

 whatever to which this function could be assigned. He, there- 

 fore, concludes that it is discharged by the elastic cuticle of the 

 hood, aided by the elevation of the tentacles which press against 

 its internal surface. 



The tentacular corona (d) is composed of the tentacles or 

 arms. 



It is an important observation that the number of the tentacles 

 increases, not only on the bud while in course of development, 

 but also on the polypide after separation from the parent, and 

 when the reproductive elements have made their appearance. 

 The number at the time of detachment is twelve ; but fourteen, 

 sixteen, and eighteen have been met with ; the latter seems to 

 be the limit. This observation shows that the number of 

 tentacles cannot be relied upon in the case of Loxosoma as a 

 specific character.^ 



The tentacles are always bent, even when most fully expanded. 

 They are not retractile, but can be partially coiled up within the 

 vestibule, and in this condition they exhibit slow, vermicular 

 movements. They are attached to the hood by a certain portion 

 of their external surface, but the inner extremity is free and 

 rounded off, and projects into the vestibule. 



The structure of the tentacles is not easily determined. 

 When viewed in profile (PI. XXII, fig. 10) a pretty thick cuticle 

 is seen to form their outer surface, and beneath this the hypo- 



' Amongst the Polyzoa generally there is great variability in the number 

 of the tentacles within the limits of a species. The sub-order Clenostomata, 

 however, offers an exception ; in this division the character is so constant 

 that it has been employed as a generic distinction. It is difiicult to under- 

 stand what special significance there can be in the presence of a few more 

 or less of these (usually) variable appendages. — TransL 



