18 C. 0. Whitman 



preserved inclividuals, and, witli perhaps the exception of figs. 6 and 8, 

 represent forms of frequent occurrence. 



It will be Seen from these fignres that the form assumed by the 

 cephalic end of the axial cell is essentially the sanie for both Rhomb- 

 ogens and Nematogens. Van Beneden found that the Rhombogens are 

 as a rule shorter thau tlie Nematogens, and this agrees with my obser- 

 vations. Biit the Rhombogens sometimes attain a length that is seldom 

 exceeded by the Nematogens. One Rhombogen, taken up from the 

 renal fluid by the aid of a pipette, and measured immediately after kill- 

 ing with aeetic acid, was 5.75mm long. I have recorded no cases in 

 which Nematogens measured more than 6 mm. 



The shorter individuals often show the greatest width just behind 

 the head (fig. 13), tapering from this point slightly towards the bind 

 end ; while in the larger specimens the width is more uniform , being 

 .08 — .10 mm for a length of 5 to 6 mm. Two large verruciform cells, 

 filled with refractive globules, and located in the posterior half of the 

 body, at opposite sides, are quite Constant in this species; but they are 

 sometimes missing both in the younger and older forms. 



5. Dieyema truncatum Whit. Figs. 51 — 59, PI. 4. 



Occurs in Sepia officinalis Lin. (here usually asso- 

 ciated with Dicyemennea gracile), in Sepia elegans 

 Blain., and in Rossia macrosoma Delle Ghiaie. Calotte 

 octamerous, small, discoid, capping the broad trunc- 

 ated ends of the parapolars, which form the greaterpart 

 of the head; its face somewhat convex in the young; 

 occasionali y so in the adult. 



The nearly equal propolars (2 dorsal and 2 ventral) 

 much smaller than the metapolars, and encircled by 

 them. The equal metapolars alternate with the pro- 

 polars, two being lateral, one ventral, and one dorsal. 

 The diameter of the parapolar coUar greater than that 

 of the body, or of the polar cap. Ectodermal cells dis- 

 posed in alternating pairs. Two terminal cells are very 

 constantly charged with refractive granules, and more 

 or less pyriform. 



Total number of ectodermal cells 22. 



Length .50 — .75mm. 



Dieyema truncatum is a very well characterized species , and dif- 

 fers more widely from D. gracile, with which it is commonly associated 



