600 SUMMAKY OF CUERENT RESEARCHES RELATING TO 



cular nucleus together with several nucleoli, and they are to be 

 distinguished from a set of smaller cells. 



A careful account is given of the succeeding stages, and a comparison 

 of them with the descriptions of other observers as to what obtains in 

 allied forms ; and the author points out that, though there is an essen- 

 tial difference between the mode of development of the marine and of 

 the fresh-water Amphipods, the results show that there is in them all 

 an intra-vitelline or superficial segmentation. The ova of the Orches- 

 tidae exhibit an intermediate stage towards the extra-vitelline or 

 discoidal segmentation. 



Passing to the " kugelformige " organ, TJljanin shows that it is a 

 local invagination of the ectoderm, the cells of which shed out a cuticle 

 which is in connection with that developed from the surface of the 

 embryo ; it is altogether comparable to the shell-gland of the Mol- 

 lusca, and, this being certain, the question arises as to whether there 

 is in the Crustacean anything homologous to the shell. Now, the shell 

 of the Mollusca is a product of the secretion of the so-called mantle, 

 which is nothing else than a local thickening of the ectoderm. In the 

 Arthropod we do not find this ; and this being so, we cannot homolo- 

 gise the cuticular investment of the Arthropod-embryo with the shell 

 of the Mollusca. The presence of this shell-gland is a distinct proof 

 of the common origin of the two groups ; but, beyond this, there is 

 little to be said. We may suppose that the common form consisted of 

 a number of equivalent metameres, had a dorsal internal shell, a dorsal 

 vessel, an enteric canal which opened at the hinder end of the body, 

 an oesophageal nerve-ring, and a ventral ganglionic chain. The form 

 now standing nearest to this hypothetical ancestor is the Chiton. 



A short account of the development of the endoderm is given, which 

 the author shows to have its origin from the cells of the "kugel- 

 formige " organ, or in other words, from cells of ectodermal origin, 

 which have wandered into the yolk. This is clearly a secondary 

 result. The mesoderm, as in all other Crustacea, is developed by the 

 cleavage of the blastoderm. 



Limulus polyphemus.* — A paper " On the Anatomy, Histology, 

 and Embryology of Limulus polyphemus" by Dr. A. S, Packard, jun., 

 may be regarded as a continuation of the author's former series on the 

 development of the king-crab.t He discusses fully the question of 

 the affinities of that puzzling animal, and combatiBg the position of 

 those zoologists who connect Limulus with the Arachnida, he sums 

 up the facts which point to the crustacean nature of Limulus as 

 follows : — 



(1) The nature of the branchiae, those of Limulus being developed 

 in numerous plates overlapping each other on the second abdominal 

 limbs (those of the Eutrypterida being, according to H. Woodward, 

 attached side by side like the teeth of a rake), while the mode of 

 respiration is truly crustacean ; (2) the resemblance of the cephalo- 

 thorax of Limulus to that of Apus ; (3) the general resemblance of the 



* Anniv. Mem. Boston See. Nat. Hist. 1880, 45 pp. (7 pis.), 

 t See this Journal, iii. (18S0) p. 947. 



