No. 2.] THE EMBRYOLOGY OF LIMULUS. 205 



observable, the beginning of the anastomosing condition of the 

 adult {cf. Fig. 55); while the proximal (internal) limb is 

 thrown into a series of four, outwardly directed diverticula 

 which are segmentally arranged and which occupy somites two 

 to five. The external (distal) limb shows fewer modifications, 

 the chief being that the excretory vescicle is relatively smaller 

 than before ; the external opening still persists and I have not 

 found out when it closes. This figure corresponds quite closely 

 to Gulland's ('85) Fig. 3, except that in his reconstruction the 

 outgrowths from the proximal limb are represented as taking a 

 sagittal direction and the anastomosing character of the inner 

 end is carried still farther, a condition doubtless due to the 

 older stage with which he worked. 



Although I have not followed it out the appearance at this 

 stage gives countenance to the view that the whole organ of 

 the adult is derived from the coelom of somite V and that the 

 apparently metameric lobes figured by Packard ('80, PI. Ill, 

 Fig. 7, copied by Lankester '84 p. 153 Fig. 3) are not the 

 remnants of the nephridia of the corresponding somites but 

 are rather the derivatives of the diverticula shown in my re- 

 construction. Besides an increase in the size of the lobes all 

 that is necessary to convert my reconstruction into the "coxal 

 gland" of the adult are closure of the external openino-, more 

 or less complete fusion of the two limbs of the duct, accom- 

 panied by an increase in the anastomoses, the result beino- to 

 convert coelom and duct into the spongy tissue of the adult, 

 the whole organ being a series of anastomosing tubes, the 

 "caeca" of Lankester. This view of the morphology of the 

 organ receives confirmation from the fact that I have seen no 

 fusion of coelomic spaces two to five while Kishinouye, as 

 already stated, finds no coelom at all, in the anterior somites 

 which are later invaded by the coxal gland. 



A word as to the external opening of the nephridium. Gulland 

 ('85, p. 5 1 3) states that it is " at the base of the coxa of the fifth 

 limb on the side next the fourth appendage and on the dorsal 

 surface." I find upon repeated examination that it is rather 

 upon the posterior side of the coxa of the fifth pair of leo-s, as 

 I stated it in my earlier paper ('85). 



