62 NOTES AND MEMORANDA, 



in order to surmouut the obstacles which oppose their passage into 

 the midst of the viscera of the Synascidians, consist of thoracic limbs, 

 which are rather long and slender, and are terminated either by a 

 single hooked claw, as in the Pohjoon, or by several, as in the Pachy- 

 nesthus. There may be further observed, in both, the cupulfe placed 

 at the base of the legs from which they emerge, which, by their con- 

 tractions and the ease with which they assume several shapes, can be 

 applied like suckers to surfaces and be fixed there, or being lengthened 

 into a point, they may serve as means of propulsion. 



Finally, it is not uninteresting to observe the mode of termination 

 of the abdominal extremity in these two Crustacea. 



In the one {Pacliynesthus) it presents an appendage armed with 

 two divergent points, in the form of a dovetail ; underneath these are 

 two other points directed perpendicularly, a combination which seems 

 to me designed to draw up or drive away objects, as is done by the 

 hoat-hooJc emj^loyed by sailors for the same purpose. 



Polyoon likewise has the extremity of the abdomen armed with two 

 claws, which instead of being flat, are rounded, short, hooked, and ter- 

 minated by a sharp point. They can also be raised, and then serve 

 for propulsion, or be lowered, and on being drawn together, seize 

 objects so as to draw them up and furnish a point of support for a 

 retrograde movement.* 



As to the alimentation of these animals, I am necessarily reduced 

 to conjecture ; but it does not seem to mo possible that they should 

 live otherwise than at the expense of their hosts, either on their 

 material, their secretions, or their eggs. 



The form of the mouth, which generally gives such valuable indi- 

 cations concerning iis use, does not here lead to any definite conclusion, 

 seeing that it can serve as well for suction as for mastication ; we may 

 therefore presume that it is employed for both purposes. It seems 

 evident that it should be so, for without that the Crustacea, who 

 cannot seek their food outside, would infallibly perish if they did not 

 find within their reach all that was necessary for them. (The species 

 are figured.) 



Improvements in Micro - photography. — Since the year 1844, 

 when the first micro-iihotographic productions of Donne and Foucault 

 appeared in the form of an atlas of microscopic anatomy, in which the 

 plates were taken from daguerrotypes, histologists and microscopists 

 have been unable to reconcile themselves to introducing photography 

 generally as an integral part of microscopic research, in spite of the 

 excellent publications of Gerlach and Benecke. Only in particular cases, 

 when the inquirer was familiar with the application of photography 

 to other purposes, lias it been applied to produce pictorial representa- 

 tions of microscopic preparations. And yet the advantages which arise 

 from such a method of delineating objects are beyond criticism and 

 universally admitted. 



The reason for this has been the complicated methods of preparing 

 the sensitive plates. There was also required not only a micro- 



* It is particularly remarkable that the greater number of parasitic Crustacea 

 which live in the interior of the ascidians, present similar dispositions. 



