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KINGSLE Y. [Vol. V 1 1 1 . 



on to the dorsal surface, begins to grow back to the dorsal 

 median line, there begins a rapid centripetal growth of these 

 septa, resulting in broad sheets of tissue which divide the 

 peripheral portion of the yolk into a corresponding number 

 of lobes, those of the first division being of course segmentally 

 arranged. Thus there are in the cephalothoracic region six 

 pairs of these lobes, while in the abdomen they are less dis- 

 tinct and less extensive and are only temporary, disappearing 

 totally at an early stage. The fact of their temporary ap- 

 pearance in this region is, however, of considerable interest. 

 A similar process of lobulation of the yolk has been de- 

 scribed by several authors for various Arachnids, and it may 

 be regarded as characteristic of the large-yolked eggs of the 

 group. It however occurs to a greater or less extent in other 

 forms. Thus, in the Crustacea the lobulation of the midgut 

 gland ("liver") is of the same character, while in the leeches, 

 as described by Dr. Whitman ('78), the differentiation of the 

 intestine and its diverticula is exactly the same. Were this 

 process of differentiation of liver, lobes and intestine to go 

 on regularly, it would result in the production of a Limulus 

 with a paired liver in each somite, each half emptying by its 

 own duct directly into the intestine. This, however, does 

 not occur. With the development of the extensive muscular 

 system of the gill-bearing appendages and the large blood 

 sinuses in that region the abdominal midgut diverticula disap- 

 pear. In the cephalothorax the primitive regularity shows 

 the following modifications. The septa do not all grow at 

 the same rate, and (Fig. 83) some are interrupted at points 

 in their growth, so that two or more lobes remain in direct 

 connection with each other. This occurs between lobes i, 2 

 and 3, and also between lobes 4, 5 and 6. At the same time 

 the inner ends of the septa become expanded by the develop- 

 ment of the muscles of the feet so that they in places run 

 together, cutting off lobes i and 2, and 5 and 6 from direct 

 connection with the central mass. In this way the six primary 

 liver lobes and the two hepatic ducts {hcp.,'^ hcp.~) of either 

 side of the adult are differentiated. A later peripheral in- 

 growth of mesoderm still farther divides up the primary 



