No. 3-] LIMULUS POLYPHEMUS. 463 



Packard . . . are not the remnants of the Nephridia of the 

 corresponding somites, but are rather the derivatives of the 

 diverticula of the duct" (p. 205). He maintains that, "besides 

 an increase in the size of these lobes, all that is necessary to 

 convert his reconstruction into the ' coxal gland ' of the adult 

 are closures of the external opening, more or less complete 

 fusion of the two limbs of the duct, accompanied by an increase 

 in the anastomoses, the result being to convert coelom and duct 

 into the spongy tissue of the adult." Mr. Gulland's account 

 does not differ materially from this, but is not as complete. 

 He speaks of septa, which grow inside the tube and divide it. 

 In one place he found " the tube continuous with connective- 

 tissue spaces, which everywhere surround the gland." 



Our own observations have shown that there is no division of 

 the fifth somite into a dorsal and a ventral portion. It is very 

 clear, also, that the nephric duct is not a transformation of the 

 ventral portion of this somite, but a special epithelial outgrowth 

 from it, and that the rest of the somite persists as the end sac 

 only. There are no segmental diverticula of the duct, and no 

 part of the duct is converted into the glandular tissue of the 

 nephric lobes. It remains practically unchanged, except in 

 length and in the number of its convolutions, as the perma- 

 nent nephric duct of the adult. The nephridial lobes are 

 derived from segmental clusters of cells which arise independ- 

 ently of the duct from the somatic layer of the second, third, 

 fourth, and fifth thoracic somites. 



It is obvious that the comparisons and conclusions of our 

 predecessors in this line of work were based on incomplete 

 anatomical and embryological data. We must still wait a more 

 thorough study of the anatomy and development of the green 

 glands, coxal glands, and shell glands of other arthropods before 

 their relations to one another can be satisfactorily determined. 



IV. Formation of the Mesoblastic Somites 

 AND Blood Sinuses. 



The Thoracic Somites. — Soon after the formation of the 

 thoracic appendages, and before the abdominal ones have 



