REVIEW. 



An Account of Reiehenbach's Researches on the early Develop- 

 ment of the Fresh-water Crayfish} By T. Jeffeky Parkek, 

 Associate of the Eoyal School of Wines. (With Plate YI.) 



Up to last year three important papers had appeared on the 

 development of Astacus : Rathke's classical monograph in 1829; 

 Lerebonllet's ' Eecherches ' in 1812, and Bobretsky's Russian 

 paper in 1873. In all these highly important results are ob- 

 tained, and these results are now supplemented, some of them 

 confirmed and others corrected, by the elaborate account of the 

 earlier developmental stages, published during the course of last 

 year, by Heinrich Reichenbacli, of Frankfort. 



Of the process of segmentation Reichenbach gives a very 

 imperfect account — an unfortunate circumstance, as the most 

 detailed description of this process, that of Lereboullet, leaves many 

 important points to be settled, and is by no means easy to con- 

 nect with the existing accounts of the same process in other 

 animals. 



According to Lereboullet, the germinal vesicle, after impregna- 

 tion, travels from the centre to the surface of the egg, becomes 

 flattened, and ruptures. The egg is then seen to be covered 

 with a delicate envelope composed of brilliant hyaline corpus- 

 cles (corpuscles plastiques) and constituting the formative 

 yolk ; the remainder of the egg consists of food-yolk. The 

 " plastic corpuscles" before long unite to form a white disc, which, 

 shortly after the egg is laid, breaks up into smaller and smaller 

 fragments, a continuous investment to the whole vitellus (mem- 

 brane generative) being eventually produced. This membrane 

 again breaks up, forming stellate masses, which become vacuo- 

 lated, the portions surrounding the vacuoles then detaching them- 

 selves and becoming converted into rounded masses, multiplying 

 by division, the " globes gcnerateurs." "While these are being 

 formed, a network appesrs on the surface of the egg, the polygonal 



^ "Die Embryouenlage und erste Entwickluiig des Flueskretses." Vou 

 Heinrich Reiclienbach. ' Zcitsclirift fiir Wiss. Zool.,' xxix Bd., 2 lleft, 

 July, 1877. 



