240 ' CRUSTACEANS. 



ity were therefore selected^ of such dimensions as necessarily leaving 

 a cavity where there was sufficient room for the specimen crawUng be- 

 tween the convex surface of the one, and the concavity of the other. 



Thus the animal being safely lodged here, the vacuity was easily 

 brought under the focus of the microscope, exposing the ova to view, 

 while the subject itself could not turn over and conceal them from the 

 observer. Here I found an extei'nal ovarium, consisting of about forty 

 yellowish ova ; besides which a very few minute in the vicinity seemed 

 to have been detached. 



The animal was then liberated. 



None of the ova were hatched during some days devoted to inspec- 

 tion. In a week, that is on July 22, the parent was free of the whole, 

 but I could not find any of the young. No opportunity has since oc- 

 curred of repeating the experiment. 



One season each of three specimens had a cluster of white ova on 

 the thorax, in the middle of September. 



The posterior extremity of the young is proportionately more ob- 

 tuse than in the parent. Further, unless it be immediately or speedily 

 consequent on production from the ova, they do not seem to undergo 

 any conspicuous metamorphosis. 



Exuviation is less frequent here than of many other crustaceans. 

 The integument, however, separates in two portions, which are nearly 

 white. 



This is an extremely pacific, tranquil creature, always seeking shelter. 



Specimens have survived many months in confinement. 



Plate LXV. 



Fig. 1. Asellus vulgaris. 



2. The same, enlarged. 



3. Group. 



4. Ovarium, enlarged. 



•5. Detached ova, enlarged. 



6. Young from the ovum, enlarged. 



