Chapter XIII.— THE EMBRYOLOGY OF THE LOBSTER. 



I shall not attempt to give a detailed account of the embryonic history of the 

 lobster, although for several seasons I have spent much time both in collecting and 

 preparing material for this purpose. I will offer only a few notes on the early 

 phases of development, and, to lend continuity to the whole, will sketch briefly the 

 changes in external form which the embryo undergoes. 



Early embryo] ogists, Eathke in particular, to whom reference has already been 

 made (160), examined the older embryos of the lobster or dissected them from the 

 egg membranes, but the only paper of this period which attempts to deal directly with 

 the embryology of the animal is that of Erdl (62), published in 1843. Erdl treats 

 of the laying of the eggs and the fastening of them to the appendages of the 

 mother; of the nature of the laid egg and of the external anatomy of the older 

 embryos; but his work was done before the modern methods of microscopical research 

 had been discovered. This pioneer observer was thus greatly handicapped and his 

 results are now of but little value. 



Smith figured and described the external anatomy of a well-advanced embryo from 

 a lobster captured May 2, 1872, at New London, Connecticut (182). This stage nearly 

 corresponds to that shown in cut 38. 



In September, 1891, a paper on the Embryology of the Lobster, by Bumpus, 

 appeared, in which the early stages, to the close of the egg nauplius period, are care- 

 fully described and illustrated by very accurate and beautiful drawings (30). 



A short account of my earliest studies appeared in 1890 (91), and this was followed 

 by additional notes in May, 1891 (92), in 1893 (96), 1894 (97), and 1895 (100). 



NORMAL DEVELOPMENT. 

 THE MATURATION AND SEGMENTATION OP THE EGG. 



In the section on the growth of the germinal vesicle I have described the only 

 stage in the maturation of the egg which has been directly observed (p. 154, plate 42, fig. 

 161), where the germinal vesicle has approached the surface and is undergoing indirect 

 division, being overtaken in the metakinetic stage. As already stated, it is evident 

 that in this particular egg the germinal vesicle was about to give off a polar body. 



Bumpus, who was the first to detect polar bodies in the egg of the lobster, gives 

 the following account of them : 



They are present in many eggs, and appear to be attached at no special point of the vitellus, so 

 far as the flattened area is concerned, being sometimes within it and sometimes without. It may be, 

 however, that I have only seen them in secondary positions ; for in some cases they seemed to move 

 freely about within the egg membrane. They were not observed in process of formation, nor were 

 they invariably present. Before the blastula is formed they disappear. (SO) 



I was unable to satisfy myself that the polar cells could be distinguished with 

 certainty, and so have not figured them. It is difficult to detect such minute bodies 

 in so large and so opaque an object as the egg of the lobster, and owing to mechanical 

 causes, possibly through the emission of the polar bodies themselves, minute spherical 

 globules of food yolk are set free and float in the fluid which underlies the eggshell. A 



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