110 EMBRYOLOGY OF THE PODOPHTHALMATA. 



that it is during the early summer months that ova are generally 

 carried in the immature state, yet there are many species that are 

 later, and others that are earlier than this. In May I obtained the 

 ova, in an immature state, of Portimiis tnarmorciis^ Palcetnon serratus^ 

 P. squilia, Porttinmus latipeSy Gebia deltura^ Scyllarus arctics, etc. 

 I had, however, already obtained the ova of several species in Jan- 

 uary, February, and March. In September I obtained the mature 

 ova of Xantho florida^ X. rivulosa, and Achceus Cranchii, and in 

 December the semi-mature ova of Hyas coa7'ctatus. It thus 

 appears that the spawning season extends, in different species, 

 over the whole year ; and that more or less favoured localities, 

 causing a variation in the spawning season of particular species, 

 may account for the discrepancy to which I have referred in the 

 second place. 



Taking as an example a species of sbmewhat wide distribution, 

 I have found that specimens from the South-west parts of the 

 English coast, and from the Channel Islands in particular, attain 

 to a more developed condition in many ways ; and it is thus that 

 we find species with ova in such favourable localities, at a time 

 when the same species from the Thames estuary or the North-east 

 coast would be without any ; hence possibly arises the difference 

 in time recorded by various authors as to the spawning-season 

 of one and the same species. 



Not only does this variation obtain under these conditions, 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-zoM^x^d. 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, Homarus marifius, are three times the size of those of the 

 spiny lobster or cray-fish, Paliminis qiiadriconiis^ although the 



