164 BENNET M. ALLEN. 



growths in each somite. Attention may first be called to the 

 place marked (C^. This is a very pronounced constriction 

 occurring similarly in each of the somites studied. It is far more 

 marked than the other constrictions in the somite. This prob- 

 ably marks the primitive metameric limits of the alimentary tract. 

 This is merely a suggestion, as a study of the embryology of this 

 form would be necessary, before a definite statement could be 

 made in regard to this point. The more prominent of the two 

 sets of pouches are those opening into the alimentary tract at the 

 posterior end of each somite. The testes (/) are situated chiefly 

 in the second and third rings, their ends projecting slightly into 

 the adjoining rings. The vas deferens connecting them is shown 

 only on the right-hand side of the drawing. 



The nephridia, shown on the left-hand side of the drawing, are 

 much coiled, extending from the nephrostome at the tip of the 

 testis lobe in the front part of the second ring, to the end of the 

 duct by which the nephridial vesicle opens to the exterior 

 through the nephropore. This nephridial vesicle lies in the fifth 

 ring of the somite to which it belongs and the sensory, or first 

 ring of the somite immediately posterior. It projects slightly 

 beyond each of the two rings named. The nephropore is situ- 

 ated in the extreme posterior part of the fifth ring. 



HULL ZOOLOGICAL LABORATORY, 

 UNIVERSITY OF CHICAGO. 



