140 PROGRESS OF MICROSCOPICAL SCIENCE. 



vember 8, 1875) by M. Korotneff, an abstract of whose essay appears 

 in the ' Academy ' (January 1876). He finds the body of these crea- 

 tures composed of four layers : (1) an ectoderm covered by a cuticle ; 

 (2) a gelatinous layer ; (3) an elastic membrane ; (4) the endoderm. 

 At the base of both endoderm and ectoderm are cells which transform 

 themselves into nematocysts, or gland-cells. The gelatinous layer 

 and the memhrana propria are traversed by elastic fibrils which are 

 prolongations of endodermic cells. Two sorts of muscles are found, 

 longitudinal and circular, the latter always forming an external layer. 

 The longitudinal muscles are represented by four trunks, which com- 

 mence at the bottom of the foot. In the middle of the body each 

 trunk divides itself into two branches, and each branch enters a 

 bundle of tentacles. A layer of muscular fibres is also found in the 

 walls of the peristome, and buccal tube. The circular muscles are 

 found round the mouth, along the margin of the body, and in the 

 tentacles. Each fibre is a simple cell, containing a highly refrin- 

 gent fibril. A single fibril sometimes traverses a series of connected 

 cells. 



Schultze regarded the bristles of the urticating organs (cnidocils) 

 as instruments of touch. M. Korotneff finds the tops of the tentacles 

 covered with the urticating nematocysts, each one placed in a cell 

 which carries its bristle (soie). The cellule is extended into a long 

 fibril, which traverses a bipolar or a multij)olar cell, and terminates 

 in a little peduncle that penetrates the memhrana propria. These 

 multipolar cells the author regards as nerve-cells, and states that the 

 analogy between the tactile organs of lucernaria and those of the 

 arthropoda is complete. 



The digestive cavity contains a stomach, and four large radiating 

 canals, and its walls are coated with a layer of endodermic cells, 

 ciliated on the peristome, and single on the external walls of the 

 body. Among these endodermic cells are unicellular glands secreting 

 a digestive liquid. The surface of the cavity is enlarged by mesen- 

 teric filaments, one side of each filament being composed of gland- 

 cells, the other ciliated. The author supposes the gland-cells produce 

 a circulation in the cavity, and that the simple endodermic cells 

 absorb the nutritive fluid. He states that the sexual elements are 

 developed in special capsules of endodermic origin. Each capsule is 

 composed of the endoderm, and of an elastic membrane {memhrana 

 propria), and is filled with ovigerous cells. A young egg has a large 

 germinating vesicle, which disappears in proportion as it grows. The 

 developed egg is surrounded by a strong membrane, and has a large 

 micropyle. The ripe capsule is furnished, near its base, with a canal 

 which serves for the exit of the sexual products. The elasticity of 

 the memhrana propria keeps this canal shut except when the internal 

 pressure of the mature eggs forces it open, after which it again 

 closes. 



The Embryogeny of the Flea. — In a recent number of the ' Academy ' 

 there is a capital abstract of a paper lately read before the French 

 Academy by M. Balbiani. It states that M. Balbiani finds the ovum 

 of Pulex felis better adapted to researches than that of other species, 



