130 REPORT — 1872. 



A system of vessels (probably water-vascular) was also described. Tbis con- 

 sists mainly of a sinus whicb surrounds tbe great apical ganglion, and sends off 

 tbree brancbes, wbicb run in a radial direction in tbe walls of tbe dome, two 

 lateral and one aboral, and appear to open into a sinus wbicb surrounds its base. 



In tbe progress of development tbe aboral end of tbe alimentary canal becomes 

 elono-ated in tbe direction of tbe axis of tbe dome, carrying witb it the walls of 

 • tbe base of tbe dome, wbicb are to form tbe proper body-walls of tbe future worm ; 

 and in tbis way a long cylindrical appendage becomes developed, and bangs from 

 tbe central point of tbe base. At first tbere is no trace of segmentation ; and tbis 

 is subsequently induced on the cylindrical body of the worm by tbe formation of 

 consecutive annular constructions. 



The process of development, as observed by tbe author in tbe species of Ilitraria 

 examined by bim, thus differs in several points from that observed by Mecznikoff. 

 Among these the most important is that tbe ventral side of the worm is formed 

 simultaneously with tbe dorsal instead of subsequently to it and independently of 

 it, as in the case described by Mecznikofi". The development of tbe worm was not 

 traced to the ultimate disappearance of tbe dome-like body of tbe larva. 



On some points in the Development of Vorticcllidas. By Prof. Allman, F.E.S. 



The author described, in a beautiful branched and clustered Vorticellidan, a 

 process different from any which bad been recorded by those observers who had 

 described the so-called encysting process and the behaviour of tbe " nucleus " in 

 tbe Vorticellidae. 



In almost everj^ cluster some of tbe zooids composing it bad become greatly altered 

 in form ; they had increased in size, and instead of tbe bell-shaped form of tbe 

 others, had assumed a globular shape, and bad lost both oral orifice and ciliary 

 apparatus, while their supporting peduncle bad ceased to be contractile. In the 

 younger ones tbe contractile space of tbe unchanged zooid was still very evident, 

 •but was fixed, showing no tendency to alteration of size, and tbe so-called nucleus 

 was very distinct and larger than in the ordinarj' zooids. The whole bad become 

 enveloped in a transparent gelatinous-looking investment. 



In a slightly more advanced stage another envelope, in the form of a brown 

 borny capsule, begins to be secreted between the proper wall of the zooid and tbe 

 external gelatinous investment. It is at first thin and smooth, but it gradually 

 acquires considerable thickness, and becomes raised on its outer surface into ridges 

 enclosing hexagonal spaces. 



In this stage tbe capsule has become too opaque to admit of a satisfactory view 

 into its interior ; but if the capsule be carefullj' opened, its contents may be libe- 

 rated so as to render apparent their real nature. It will be then seen that these 

 consist of a minutely granular semifluid plasma surrounding tbe " nucleus," which 

 has much increased in size and occupies a large portion of the csivity of tbe cap- 

 sule. Tbe condition of the contractile space coidd not be determined ; it has pro- 

 bably altogether disappeared. 



In a further stage tbe " nucleus" has undergone an important change ; for in- 

 stead of tbe long cylindrical form it had hitherto presented, it has become irregu- 

 larly branched, has acquired a softer consistence, and has, moreover, broken itself 

 up into two or more pieces. Tbis change in the " nucleus " is invariably accom- 

 panied by tbe appearance of nucleated cell-like bodies, which are scattered through 

 the corpuscular plasma which had filled the rest of the capsule ; they are of con- 

 siderable size, of a spherical form, and witb their nucleus occupying tbe greater 

 part of their cavity, and having its nucleolus represented by a cluster of granules. 



In obber capsules, apparently tbe more advanced, no trace of tbe so-called nu- 

 cleus of the vorticella-body could be detected ; and it seems to be entirely replaced 

 by the spherical nucleated cells, which had now still further increased in number. 

 It is impossible not to regard these cells as tbe result of tbe disintegration of the 

 "nucleus ;" and the conclusion is a legitimate one that they are finally liberated by the 

 natural dehiscence of the capsule, and become developed into new Vorticellidans, 



