306 BULLETIN OF THE 



The gluey secretion which attaches the eggs to the abdominal limbs of 

 the mother hardens into a structureless membrane, which invests each 

 egg so closely that it is difficult to separate it from the proper egg- 

 membrane. The yelk is of a greenish color, heavily charged with deuto- 

 plasmic elements in the shape of minute granules and larger spherical 

 vesicles, intermixed with oil-globules. 



The cleavage of the egg begins in two planes almost simultaneously. 

 These planes are at right angles with each other, passing through 

 the long and the short axes of the egg. The egg is thus divided into 

 four cleavage-spheres, each provided with a nucleus and nucleolus. 

 Delicate lines of protoplasm extend like rays from the nuclei into the 

 surrounding yelk (PI. I. Fig. 1). 



The opacity of the eggs prevented my determining whether the 

 cleavage passed completely through the yelk.* 



The cleavage proceeds regularly (Plate I. Fig. 2), forming eight, six- 



* Bobretzky, who has made sections of the eggs of Palcemon, is uncertain how 

 deep the clefts enter the yelk in the earliest stages of segmentation, owing to the 

 imperfection of his sections. (On the Embryology of Arthropods [in Kussian]. Zapiski 

 Kiefs. Obshtshest. Yestestvoispitatalyei, Vol. III. p. 190. 1873. A short and unsat- 

 isfactory abstract of Bobretzky's paper, in German, by Hoyer, appears in Hofmann 

 and Schwalbe's " Jahresberichte," Vol. II. pp. 312-318. 1875. I have had certain 

 parts of the original paper translated from the Kussian for me by Mr. Ivan Panin.) 

 By the time that 128 cleavage products are formed they have the shape of long pyra- 

 mids, whose apices are fused in the common undivided granular mass at the core of 

 the egg, while the clear protoplasm, involving the nuclei, collects at the surface of 

 the egg, in the bases of the pyramids. Later the boundaries of the pyramids become 

 obliterated, and their protoplasmic bases thus form a cellular superficial blastoderm, 

 enclosing the opaque nutritive yelk (PL V. Fig. 18 et scq.). 



In Crangon vulgaris, according to E. Van Beneden (Recherches sur la Composi- 

 tion et la Signification de l'CEuf. Mem. Cour. Acad. Roy. Belg., Vol. XXXIV. p. 

 142, PI. X. Fig. 20. 1870), the cleavage is at first total, then a separation takes place 

 between the deutoplasm and the protoplasm of the vitelline segments ; the former 

 accumulating at the centre of the egg, the latter, carrying with it the nuclei of the 

 segments, is borne to the periphery to constitute the cells of the blastoderm. 



The egg ofPeneus {membranaccus?), as observed by Haeckel (Die Gastrulaund die 

 Eifurchung der Thiere. Jenaische Zeitschr. f. Naturwissenschaft, Vol. IX. pp. 447, 

 448, PI. XXIII. Fig. 82), in the stage with four cleavage-cells, showed on cutting 

 that the furrows extended less than half-way to the centre of the egg, leaving a large, 

 elliptical, central mass of nutritive yelk undivided. 



In Eupagurus Prideauxii, as we learn from P. Mayer (Zur Entwicklungsgeschichte 

 der Dekapoden. Jenaische Zeitschr. f. Naturwissenschaft, Vol. XI. p. 212, PL XIII. 

 1877), eight segments, completely separated from one another, are formed before the 

 segregation of the deutoplasm from the protoplasm begins. 



