ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 373 



and the whole fibre is divided into blocks separated by empty spaces within 

 the sarcolemma. In the blocks the transverse strise are very closely 

 approximated. These ruptures are the result of violent convulsive tension 

 between the contracted and the adjacent passive portions. The first pads 

 of contraction are the consequences of a mechanical excitation of the 

 isolated fibre ; the spreading of the contraction is due to the gradual imbi- 

 bition of a foreign irritant fluid in the interstices separating the fibrils. 

 The appearances thus artificially produced are strikingly like those seen in 

 the dead muscle of typhoid, variola, and cholera patients. In fishes, 

 chelonians, birds, and mammals, the direct imbibition is so rapid that the 

 preliminary contracted pads seem to be absent. Annular swellings appear 

 separated by constrictions, and forming an irregular transverse striation. 

 Even in muscles apparently quite rigid, after some days, in frogs and 

 lizards, living and contractile fibres may be found among the dead. At the 

 commencement of rigidity the same mixture may be observed in mammals. 

 Elasticity and contractility are lost at the same moment. 



B. INVERTEBRATA. 



Singular Parasite on Firola.* — Dr. J. Barrois describes a unique 

 parasite found on the surface of Pterotrachea coronata in the Gulf of Ville- 

 iranche. The body of the animal was red and opaque, the form triangular, 

 the structure unique. 



(1) The alimentary system consists of three distinct sacs, opening 

 separately to the exterior at the ends of the arms. They were capable of 

 suction by means of three muscle bundles inserted on three hyaline cords 

 adhering to the wall of the sacs. Each sac exhibited a thick epithelial 

 lining surrounded by a strong muscular envelope. (2) A water-vascular 

 system was present, communicating with the interior and with the cavity 

 of the sacs via the terminal claw. A partitioned central organ gives off 

 three canals radiating to the ends of the arms. (3) The integument con- 

 sisted of an external cuticle, an epithelium, rounded mesenchymatous cells, 

 and an internal more delicate cuticle. (4) The claw at the end of each 

 arm exhibited three chambers, communicating on the one hand with the 

 endodermic sacs and the water-vascular system, and on the other with the 

 exterior by means of a single terminal aperture. (5) There is a nervous 

 system consisting of a thick trunk connecting the sensory plates formed by 

 a thickening of integument at the root of each arm in the concave portion 

 of the disc. Two fi.brous cords extend from the dorsal face to the mass of 

 areolar tissue above the partitioned central organ. They are bounded to 

 right and left by an albuminous nucleated mass. The skeleton was un- 

 fortunately lost in preparation. 



The only suggestion that Dr. Barrois can offer is that this unique form 

 is possibly an Echinoderm modified by parasitism, or that it ought to be 

 referred to a new but allied division. 



Pelagic Micro-organisms of Fresh-water Lakes.j — Of late years 

 several authors have described the numerous kinds of vegetable and animal 

 organisms living in the pelagic region of lakes. M. H. Forel corroborates 

 Asper's statement | as to the predominance of certain forms on different 

 days, in the Lake of Geneva. " The rich development of micro-organisms 

 leads to a better understanding of the cycle of life in the pelagic region 

 of the lake." 



* Journ. (le I'Anat. et de la Physiol., xxiii. (1887) pp. 1-17 (2 pis.), 

 t Arch. Sci. Phys. et Nat., xvii. (1887 J pp. 60-2. 

 X See this Journal, 1887, p. 53. 



