20 C. 0. WhitmaQ 



the young, and D. gracile as the adult, of Dicy emina KöUikeriana ; and 

 he very naturally iuferred that the nine polar cells of the mature forms 

 must be present in the so-called »young- individuals « . Bearing this 

 fact in mind , it is easy to see what parts of the ahove description were 

 actually drawn from a study of D. truncatum. The smallness and obliq- 

 uity of the calotte are attributes belonging to this species, while the 

 number and, in the main, the disposition of its cells are applicable only 

 to D. gracile. 



The description of the parapolar cells (p. 20 — 21) accords nearly 

 with my own observations. »These cells are two in number, and differ 

 from each other neither in form nor volume, nor in any other character. 

 They are distinguished from the ectodermal cells of the trunk by their 

 form and Contents. In well developed individuals, they are nearly ellip- 



tical in optical section (pl. 1, flg. 14) The small axis of the 



ellipse is about equal to three fourths of the large axis. The Contents 

 of these cells is much darker than that of the ectodermic cells of the 

 trunk; li is finely granular, but never charged with the refractive glob- 

 ules which are almost constantly met with in the other cells of the 

 ectoderm, and which, by accumulating, produce warts (verrues) . 



These two parapolar cells are placed on the lateral faces of the 

 head. They meet along the median dorsal and the median ventral line, 

 thus forming a collar, through which passes the endodermic cell. Each 

 constitutes a moiety of the ring. This ring is much shorter at the dorsal 

 and the ventral line of junction than at the sides of the head. The 

 ectodermal cells of the trunk , which immediately follow the parapolar 

 cells , end in a point between the latter, but never reach the cells of the 

 polar coiffe.« 



I have never observed the strong contrast here said to exist be- 

 tween the Contents of the parapolars and that of the other ectodermal 

 cells ; and I should say that the form of the parapolars , seen in optical 

 section, is triangulär rather than elliptical. 



With reference to the inclination of the calotte , I do not see how 

 Van Beneden's figure 6, PI. 1 cau be reconciled with his Statements. 

 Jndging from the position of the parapolars , this figure represents the 

 head as seen from the right , or left side ; but how, in either case , can 

 the calotte be said to incline to the ventral face? Again, taking the 

 size of the propolars as a means of orientation — allowiug the ventral 

 cells to be smaller than the dorsal — the calotte appears to be seen 

 from the dorsal face , and to be incliued towards this face , all of which 

 is equally coutradicted by the position of the parapolars. As I have 



