OF ARTS AND SCIENCES : FEBRUARY 14, 1865. 401 



viz. early last December, the genital organ invariably laid transverse 

 to the longitudinal axis, and occupied a very large portion of the bulk 

 of the posterior end of the body. Most frequently it had a U-shaped 

 form (fig. 3, n), and embraced the contractile vesicle with its two limbs. 

 It was then of a yellowish brown color and perfectly homogeneous. 

 Occasionally it was observed to be divided into three or four masses, 

 which extended toward the region encompassed by the posterior annu- 

 lar furrow. While in the U-shaped form the whole semi-opaque mass 

 was enclosed in a transparent envelope (?ie). Oftentimes there was to 

 be seen immediately over and close to the dorsal region of the nucleus 

 and directly in the plane of the axis of the body, a minute, clear, ves- 

 icular corpuscle (fig. 3, t), which seemed to have the character of a 

 "nucleolus" or — as is now becoming the belief, since the investiga- 

 tions of Balbiani and Claparede — a testicle. 



Reproduction from the egg has not been observed, but transverse 

 division occurred in a number of instances. In the latter case it 

 agrees, in the process, with what Allman, loc. cit., has described, ex- 

 cepting that the resultants (fig. 6, I., II. ; fig. 7) are quite different in 

 their proportions from the adults (fig. 1, 2, 3). At the moment of 

 separation the young offshoot (fig. 7) is about two thirds the size of 

 the adult, and is almost as broad as long, and bulges strongly on the 

 ventral side (Y), in front of the mouth (m). It has a very flat ante- 

 rior end, and the pseudo-cuirass (joc) of this part is represented by an 

 inconspicuous unguiform body. The anterior transverse furrow, on 

 account of its narrowness, hardly attracts attention, except along its 

 ventral edge (of), where it is rendered conspicuous by the strong pro- 

 jection of the unguiform cuirass. As in the adult, it is broadest ven- 

 trally, but, growing shallower, thins out (o/^), going dorsally, to almost 

 nothing. The relations and structure of the various organs, cilia, &c. 

 are the same as in the full-grown individuals ; but with progressing 

 growth the proportions of the diverse regions of the body change in- 

 sensibly, as may be seen by comparing figures 7, 4, and 1, which are 

 respectively representatives of the youngest, middle-aged, and adult in- 

 dividuals. 



Description of Figures. 



In all the figures the same letters refer lo corresponding parts. 



A. The anterior end of the body. P. The posterior end. 



D. The dorsal side. V. The ventral side. R. The right side. 



L. The left side. 



