ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 587 



lacustrine forms inhabited fjords and more or less deep bays which 

 gradually lost their communication with the sea ; the waters, which became 

 less and less saline, were finally quite fresh, but they retained such of the 

 animals as were able to adapt themselves to the new conditions of existence ; 

 it is because of this process that we find the same species in the sea as in 

 fresh-water lakes. 



Phylogeny of Bopyridae.* — MM. A. Giard and J. Bonnier, limiting 

 themselves for the present to European Decapoda, point out that each species 

 of these Crustacea may have two or three distinct parasites ; the Bopyridae 

 parasitic on the Decapoda may be divided into three groups — abdominal, 

 branchial, and visceral parasites ; analogous cases may be cited among the 

 Branchiobdellidse of the crayfish and the CEstridse of deer and horses. 



These facts, incomprehensible on the theory of the fixity of species, 

 seem to show that several states of symbiotic equilibrium have been succes- 

 sively realized ; by the aid of development these can be traced in the case 

 of the Bopyridse. 



The first larva is very uniform throughout the group, and its long 

 pelagic existence shows us that the ancestors of the Bopyridse were free 

 forms; by the whole of its organization it approaches the (Egidae, and 

 more particularly Eurydice. The second larva is of the Cryptoniscus-sta.ge, 

 and it is now that the parasitic life begins ; in the Cryptoniscidae the male 

 is arrested in its development at the second larval stage, but in the other 

 Bopyridae it takes a more or less Idothea-like form. 



The singular coexistence of parasitic Cirripedes in all the types of 

 Decapods infested by the Bopyridae leads us to suppose that the Bopyridae 

 have been introduced into the Decapoda by the Cirripedia Ehizocephala ; 

 while the members of one branch of the Cryptoniscidae have remained 

 faithful to their first host, another branch has become adapted for direct 

 parasitism on the Decapoda, and has given rise to Phryxtis, Bopyrus, and 

 the Entoniscidae. The presence of a phryxoid stage in the development of 

 most female Bopyridae shows that the genus Phryxus may be regarded as 

 the stock whence many have issued. 



Muscular Fibres of Edriophthalmata.t — Dr. E. KcBhler has investi- 

 gated the mode of grouping of the contractile elements in the muscle-fibres 

 of Isopoda and Amphipoda, as well as their relation to the cells from which 

 they are developed. A large number of forms were examined. The con- 

 tractile substance occupies the central region of the primitive bundle, while 

 the protoplasm not differentiated into fibrils forms a peripheral envelope. 

 It may form a layer more or less thick, but its situation in relation to the 

 contractile element is always the inverse of that which is observed in the 

 muscles of other animals. The variations in the different forms concern 

 the size of the muscle-cells and primitive cylinders, the number of the 

 cylinders, the form, development, and relative importance of the contractile 

 element, and finally the number, size, &c., of the nuclei. The size of the 

 muscle elements is not proportionate to that of the animal. As regards 

 the above variations, Amphipods are much more regular than Isopods. 



Copepod Parasite of Amphiura squamata.J — M. A. Giard describes 

 the female, male, and young forms of Cancerilla tuhulata Dalyell, which he 

 found at Fecamp as a very abundant parasite on Amphiura squamata. 



(a) The female, which is generally fixed to the oral face of the disc, at 

 the base of a ray, with its head towards the mouth, has a triangular form, 



* Comptes Eendus, civ. (1887) pp. 1309-11. 



t Journ. Anat. et Physiol, xxiii. (1887) pp. 113-23 (1 pi.). 



j Comptes Rendus, civ. (1887) pp. 1189-92. 



2 Q 2 



