OBSERVATIONS ON POLYZOA. 213 



longation of the outer membranes of the stomach, connect- 

 ing the lower end of that organ with the bottom of the 

 cell in the vicinity of the bases of the retractors. 



The researches of Mr. Hancock, upon the early devel- 

 opment of the statoblast, which he supposed, in common 

 with other observers of that time, to be a true ovum, and 

 those of Prof. Allman, give an almost complete history of 

 their growth.* The former found them in Plumatella and 

 Fredericella, in the interior of the funiculus, as large nu- 

 cleated cells ; and the latter, apparently begining his inves- 

 tigation at a later period, as a mass of smaller cells, which 

 must have resulted from the division of the primary cell 

 of Mr. Hancock. 



They arise within beafl like swellings of the funiculus, 

 and, enlarging slowly, push out to the surface of the chord, 

 and upwards towards the stomach, until finally they hang 

 upon the exterior, arranged alternately on either side, the 

 youngest being at the lower end (PL 8, fig. 2, W). 



According to Prof. Allman the contents increase in bulk 

 by the formation of new cells, and are enveloped in a 

 cellular membrane (Fig. 1, a) with an outer gelatinous 

 envelope (PI. 8, fig. 2, W""). Between these, two other 

 membranes are secreted, one of which constitutes the horny 

 sheath, and the other the annular ring of the statoblast 

 (PI. 8, figs. 7, 8, 9, W, W"). This sheath and the annulus 

 gradually assume a distinct cellular structure, and a horny 

 consistency ; the former at the same time acquiring a deep 

 brown color, and the latter a brilliant golden hue. 



The contents of the statoblast are often contracted, and, 

 while in this condition, during the earlier stages of de- 

 velopment before the horny casing becomes too opaque, the 

 membranes may be analyzed by the aid of the microscope. 



The interior cells are large and colorless. They are 

 surrounded by a thin, homogeneous membrane, which, 

 when the cellular contents are reduced by contraction, 

 seems to be drawn out into numerous, minute, conical pro- 

 jections at the points where it is attached externally to the 

 overlying membrane (Fig. 1, b). I was unable on account 



*ALBANY HANCOCK. Ann. Nat. Hist. Vol. 5. p. 190. 



ESSEX INST. PROCEED, iv. BE. March, 1866. 



