JENNINGS : DEVELOPMENT OF ASPLANCHNA HEEKICKII. 89 



a testis. Again, in his Eotatoria (Wrotki) Galicyi, "Wierzejski ('92^) 

 gives a figure of the entire animal, with special figures of the character- 

 istic glandular organ, the trocbal field, the jaws, and the excretoiy 

 system, together with a brief description in the Polish language. 



Asplanchna Herrickii was afterward reported by the autlior (Jennings, 

 '94) as occurring in Lake St. Clair, and by Levander ('95) as occurring 

 in the neighborhood of Helsingfors. 



2. Development. 



The unsegmented egg of Asplanchna HeiTickii is similar in form to 

 that of Callidina russeola, investigated by Zelinka, but slightly smaller, 

 the maximum dimensions in Callidina being 130 /a by 90 yu,, while the maxi- 

 mum dimensions observed in Asplanchna Herrickii were 97 /j. by 83 /x,. 



No thick-shell "winter eggs" were ever observed by me in the 

 specimens taken ; possibly later in the fall these would have been 

 found. 



In regard to the details of the developmental process, reference must 

 be made to Part First ; the purpose hei'e is merely to point out such 

 observations as are of importance from the standpoint of rotifer 

 morphology, noting especially any dififerences between my account and 

 those of other writers. 



A. Maturation. 



As stated on page 13, the place of polar-cell formation in Asjtlanchna 

 has a different relation to the axes of the egg from that ascribed to it by 

 Zelinka in Callidina. In the ensuing discussion I shall, for convenience 

 of comparison, use the orientation adopted by Zelinka ; that is, what I 

 have called the " macromere end " is anterior, the " micromere end " 

 posterior. That side of the egg upon which later the blastopore is 

 found, occupied in early stages ciiiefly by the quadrant D, is ventral, the 

 opposite side dorsal. These terms have no .constant relation to the 

 terms of orientation employed in Part First. 



As previously described and figured (Plate 1, Figs. 1 and 2), the polar 

 cell is formed near one of the ends of the ellipsoidal egg, and the place of 

 formation is cut by the first and second cleavage furrows (Figs. 6 and 8). 

 The same is true for Asplanchna priodouta. 



In these two species of Asplanchna, therefore, the place of polar-cell 

 formation is the same, with reference to the form of the egg, as that 

 described by Lameere ('90) f^r Asplanchna Sieboldii, and by Zelinka 

 ('91) for Callidina Leitgebii (p. 53) and Melicerta ringens (p. 117). In 



