228 M. GOSSE. 



hovering round them, and ready to devour them the 

 instant weakness or injury prevents their keeping in 

 motion the cilia, which serve both for locomotion 

 and defence. Let them cease to move, a regular 

 attack is made, and the animal is soon devoured ; 

 and it is interesting to observe several of the scaven- 

 gers sporting with the empty shell, as if in derision 

 of the havoc they have made. 



The same difficulty of calculation does not exist, 

 at least to any such extent, with the spawn of Eolis, 

 which is laid in stringy coils. M. Gosse mentions 

 a specimen of E. papillosa that laid nine strings of 

 spawn in his tank between the 20th of March and 

 the 24th of May, all as nearly as possible of the 

 same length. Each string contained about a hun- 

 dred convolutions, each convolution about two hun- 

 dred ova, and each ova including, on an average, two 

 embryos, making a total progeny of forty thousand, 

 produced from one parent in little more than two 

 months. 



I may mention that on no occasion have I ever 

 found the spawn coils of either Doridise or Eolidida) 

 in my tanks, or at the sea-shore, except during the 

 months of January and February or March ; neither 

 have any of my specimens spawned more than once 

 during an entire season. From noticing the same 

 group of parent slugs congregated, and remaining, as 

 I can affirm, for weeks near their egg clusters, evi- 

 dently in a most enfeebled condition, it has occurred 



