42 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tion witli that of Faxon, on the development of Pahemonetes vulgaris* 

 and with Fritz Miiller's preliminary notice of Palcemon potiuna.'\ 

 An introductory account of the literature of Palcemonetes and allied 

 Crustaceans is given by Dr. Mayer, who also notes at the end of his 

 paper some general considerations of much interest. 



The development of this fresh- water species of PalcBmonetes is 

 more like that of the fresh-water Pcdcsmon than that of the marine 

 Palcemonetes. As with P. potmna, the embryo leaves the egg in a 

 comparatively advanced condition, furnishing another instance of the 

 abbreviated development so often observed in fresh-water forms 

 when contrasted with their nearest allies found in the sea. 



Dr. Mayer maintains, against Balfour, that Claus was right in 

 rejecting the ingenious hypothesis of a palingenetic zooea, first 

 suggested by Fritz Miiller. Putting the Cumacea and Arthrostraca 

 aside, and admitting the common plan of the true zooeae of crabs and 

 Macrourous Crustaceans, Dr. Mayer does not believe that these Deca- 

 j)od-zoce8e and the very different pseudozooete of Stomopods and Schizo- 

 pods had a common progenitor (in any near sense of that term). 

 Granting their resemblances, these diverse zooegB represent not a 

 lapsed adult, but an ancestral larva. Again, the develoi:»ment of the 

 Penasidse strongly favours the view that the zooea is really a cseno- 

 genetic form, the true relations of which to the ^lysis-stage do not 

 seem to have been rightly apjn-ehended by Balfour. 



Nauplius Form of Leucifer.j — Professor W. K. Brook's observa- 

 tion on this Podophthalmate Crustacean are of considerable impor- 

 tance, owing to the fact that Fritz Miiller did not raise the young of 

 Penceus, but only inferred their relation from the observations due to 

 collections made by dredging. We have now, however, absolute 

 proof of the Naupliiform stage in one podophthalmate Crustacean. 



The eggs of Leucifer are, it is very interesting to note, developed 

 in what Professor Haeckel has called the archi-gastrula mode, a mode 

 which, it may be remembered, is found, among others, in the simplest 

 Vertebrate — Amphioxus. The Ncmplius is not specialized and peculiar, 

 as is that of Peiiceiis, but is typical, and very much like that of a 

 barnacle or of a Cyclops. The eggs of the highly specialized Decapod 

 Libinia have been followed out in their develojjment by Mr. Wilson, 

 who finds that in them the record is so compressed that the zooea when 

 it leaves the egg has the full number of appendages. Some importance 

 has been given to the skin shed by the zooea, which has been regarded 

 as being a Nauplius-skin. Mr. Brooks now shows that the Nauplius 

 itself sheds a similar skin after leaving the egg. 



Polar Globules in the Ovum of the Crustacea.§ — Grobbenisthe 

 only author who has hitherto noticed the presence of polar globules 

 in the ovum of the Crustacea. He states that he saw, in the ovum of 



* Bull. Mus. Comp. Zool. Cambridge, U.S.A., v. (1879) No. 15. 

 t See this Journal, iii. (1880) p. 630. 

 t Amer. Natural., xiv. (1880) pp. 806-8. 



§ Bull. Soc. Philom. Paris, 1880, April 10. See Ann. aud Mag. Nat Hist., vi. 

 (1880) p. 465. 



