NOTES AND MEMOKANDA, 61 



to Schindler there is no constancy in the occurrence of the diflferent 

 forms of cells, and moreover all of them contain the characteristic 

 ui'inary concretions. 



The urinary epithelium of insects contains none of the so-called 

 Dauer-zellen or long-lived cells, but renewal of the cells takes place 

 either by division, or (probably) by the nucleus of a cell which has 

 undergone dehiscence, enlarging to form a new cell, its nucleolus 

 becoming the nucleus of the latter. 



Parasitic Crustacea. — M. Hesse gives the name of Pachjnesthus 

 violaceus and Polyoon luteum to two new parasitic crustaceans of 

 microscopic dimensions (1-2 mm.), two females of which were dis- 

 covered in the harbour at Brest, enclosed in the interior of a comjiound 

 ascidian. The genera are new. M. Hesse remarks * in regard to their 

 life-history: — 



The completely stationary and so to speak secluded existence, to 

 which these Crustacea are condemned, does not requrre, as in the case 

 of those which live in a free condition, perfect means of locomotion 

 for which they would have no use ; those which they do possess are 

 rather destined to serve for creeping than swimming. 



Constantly shut up in an extremely limited enclosure formed of a 

 more or less hard test of cellulose, they are obliged, in order to move 

 in these narrow dwellings, to make themselves a passage by main force 

 and as Professor Giard has very well observed in his remarkable work 

 on Synascidia, they are obliged to make galleries, by means of which 

 they introduce themselves into the viscera; they penetrate into the 

 ovaries, and produce such disorders as often cause the death of the 

 whole colony, and might lead to the belief in the existence of a new 

 species, although these modifications are only the result of the dis- 

 turbances which they have produced in the individuals. 



This work of burrowing, which I will compare to that of the mole 

 cricket, results in the disappearance of the common cloacfe and their 

 replacement by small openings very near together, the utility of which 

 to these Crustacea is easily conceived. Without these issues, in fact, 

 the young embryos could not quit the enclosure nor disseminate them- 

 selves, and thus contribute to the dispersion of their species, and the 

 males would be imprisoned and reduced to a state of captivity which 

 is evidently contrary to the role which they have to fulfil, if I judf^e 

 from Crustacea closely allied to these, with which I am acquainted, 

 and which are extremely agile and provided with all necessary means 

 of swimming with facility. 



Moreover, this liberty which the males enjoy easily explains their 

 rarity, or rather the difficulty which there is in procuring them. 

 They are rarely sedentary. It is of course on this account that they 

 are more seldom met with than the females, which are condemned 

 to live always in confinement. These latter are besides rather difficult 

 to see, by reason of their extreme smallness ; and if it were not for the 

 eggs, which are generally of a very marked colour and which denote 

 their presence, they would often not be seen. 



The means of locomotion with which these Crustacea arc endowed 

 * ' Auu. des Sci. Nat. Zool.,' Cth ser., vol. vii. p. 7. 



