130 Mr. E. Lovett. 



but the geological features of a district have a most marked 

 result upon the life inhabiting it ; for instance, the protected 

 rocky caves and chasms, or the Zostera covered pools of a 

 granitic locality are far more conducive to the development in 

 every way, of a species, than the cold and unfriendly clay 

 shores of the estuaries of the Thames or Medway, or the 

 cretaceous ledges of the South-east coast ; hence we find the 

 ova or zooea stages of Crustacea in a more advanced state in 

 the former localities than in the latter. 



We have next to consider the remarkable disparity that 

 exists in the size of the ova of some species as compared 

 with others. 



To take a familiar example ; the eggs of the common 

 lobster Homanis marinus are three times the size of those of 

 the spiny lobster or cray fish Palimtrus qiiadricornis, although 

 the latter animal exceeds the former in size. Besides this 

 marked example there are numbers of others ; the ova of all of 

 the Palamonidce or prawns, are far larger in proportion to the 

 size of the animal than the ova of any of the Brachynra ; and 

 those of the " burrowing shrimp " Axitis stirhynclnts, an animal 

 only three or four inches in length, are even larger than those 

 of the spiny lobster, which is usually over a foot in length. 



It would seem, however, that the size of the ova may to some 

 extent be regulated by the same law that regulates the pro- 

 tective power which the parent Crustacean is able to afford to 

 its ova during development. These, I think, depend, if not 

 entirely, at any rate to a great extent, upon the conditions under 

 which the animal exists, so that a deep water species of 

 sluggish habits, or a species that passes most of its life either 

 in sand banks or mud banks will have larger ova with a 

 smaller amount of protection than a species living on the shore, 

 subject to the rough treatment of the surf, or one swimming 

 near the surface, and exposed to the disturbing influence of the 

 waves and wind. As examples of this we find that the pro- 

 tective segments of Corystes cassivelanmis, a crustacean 

 inhabiting loose sand in deep water are by no means so 

 developed as those of any of the species existing under a less 

 quiet condition of things, those of the Porttinidcr, or swimming 

 crabs, being very broad, and thus capable of affording the 

 necessary protection to the spawn carried beneath. Again, 

 we find that when the abdominal segments are broad, the 

 ligatures by which the ova are connected together, and to the 

 base of the swimmeret are more slight than when those 

 segments are narrower, in an animal existing under equally 

 favourable conditions. 



The protection referred to consists in the Brachyura of 

 broad pear-shaped somites which, as we have seen, fold beneath 



