952 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Shell of Hermit-crab.*— Mr. A. H. S. Lucas, commenting upon the 

 usually accepted statement that hermit-crabs appropriate empty shells for 

 protecting the defenceless part of the body, instances a case in which he 

 observed the crab attack a living Fasciolaria, which it pulled out piece- 

 meal after some time. From the appearance of the shells of tropical 

 species of hermit-crabs Mr. Lucas is led to think that living rather than 

 empty shells are usually seized. 



Polar Globules in Isopoda.f — Herr G. Leichmann has observed the 

 formation of two polar globules in Asellus aquaticus, and so has established 

 an example of the ovum of a Malacostracan, richly provided with yolk, 

 developing in the ordinary manner. As the presence of a nucleus in this 

 stage has been denied by some writers the author desires to put its exist- 

 ence on record. 



New Type of Compound Eye.J — Mr. F. B. Beddard finds that in the 

 retinula of Serolis there are only four cells. The rhabdom is not imbedded 

 between them, but is only in contact at its upper part ; the lower portion 

 is surrounded by two large spherical transparent cells, which fit in closely 

 between the four retinula-cells. The author has been able to find these 

 hyaline cells in several species of Cymothoidas. ^ga has seven cells to 

 each retinula, but the presence of the hyaline cells tends to confirm the 

 view of many carcinologists as to the close relationship between the 

 Serolidse and the Cymothoid^. 



Pale variety of Asellus aquaticus. § — Dr. E. Schneider gives the 

 name of Asellus aquaticus var. Fribergensis to a pale variety of A. aquaticus, 

 which has been found in the caves of Freiberg. The author considers that 

 this new variety is of great interest as representing an intermediate stage 

 between the two very closely allied species A. aquaticus and A. cavaticus. 

 Another point of importance is the support afforded to the belief that forms 

 which have become accommodated to subterranean life have a tendency to 

 resort to young or embryonic conditions. 



In A. aquaticus the pigment is well developed, and the general colour of 

 the animal is, therefore, a deep brownish grey ; its variety and A. cavaticus 

 have no pigment, and are consequently milk-white in colour. The eye of 

 A. aquaticus consists of four well-developed ocelli, almost imbedded in a 

 continuous pigment-mass, and over each there is a closely connected and 

 distinct cornea ; in the variety the pigment-mass is by no means continu- 

 ous, the cornea is indistinct and not closely connected with its ocellus ; 

 A. cavaticus has no eyes. The outer antennae of A. aquaticus have about 

 60 joints, the variety 50-60, and these are more delicate and elongated ; 

 the other species has from 25-55. A. aquaticus and its variety have 

 four coarse tactile setae on the endopodite of the first pair of maxillae, 

 A. cavaticus has five, one of which is larger than the rest. The pedes spurii 

 of the variety stand almost midway between those of the two species. The 

 cuticular calcification of A. aquaticus is slight, and there are not many 

 crystalline elements as there are in the variety, where, as in A. cavaticus, 

 the calcification is well marked. In the characters of its long hepatic 

 tubes the variety resembles the species with which it is associated. The 

 excretory organ of the adult A. aquaticus forms a continuous tube on either 

 side of the digestive heart, while in the variety these are more broken up, 



* Trans. Koy. Soc. Victoria, xxii. (1886) pp. 61-3. 



t Zool. Anzeig., x. pp. 533-4. 



: Ann. and Mag. Nat. Hist., xx. (1887) pp. 233-6. 



§ SB. K. Preuss. Akad. Wiss., 1887, pp. 723-42 (1 pi.). 



