GENUS UROGLENA. 415 



of gradation from a simply quiescent but non-encapsuled stage up to subdivision into 

 two, four, or eight spheroidal segment-masses or sporular elements. These spores 

 becoming distributed throughout this common gelatinous matrix, speedily acquire 

 the adult forms and characters, and are in most instances provided with the two 

 lateral colour-bands and eye-like pigment-spot at or immediately succeeding their 

 earliest appearance. In the majority of the specimens examined this mode of re- 

 production was alone observed^ and is chiefly to be seen in the two colony-stocks 

 delineated at PI. XXIII. Figs. 4 and 5. Not unfrequently, however, examples were 

 met with which enclosed supplementary spheroidal structures, having a diameter of 

 two or three times that of the bodies of the adult zooids, three of these being 

 included in the colony-stock illustrated by Fig. 4. On making a closer investiga- 

 tion it was found that these supplementary structures consisted of aggregations of 

 spore-like bodies contained within a hard and glass-like transparent membrane or 

 sporocyst, which exhibited its brittle consistence by rupture under artificial pressure 

 into a number of angular fragments, as shown at PI. XXIII. Figs. 10 and 11. The 

 sporular elements thus liberated from their indurated capsules were found to possess 

 two entirely distinct dimensions, being in the one instance, Fig. 11, of compara- 

 tively large size, the i-6oooth of an inch in diameter, while in the second case, 

 Fig. 10, they did not exceed the i-2o,oooth of an English inch. Not improbably, 

 however, these smaller sporular bodies represent a further segmented phase only of 

 the larger ones, and in both instances they are so minute as to merit the designation 

 of "microspores" in contradistinction to that of " macrospores," which may be 

 appropriately applied to the structures derived from the simple segmentation into 

 two, four, or eight sporular elements of the ordinary unencapsuled zooids, as 

 previously described. The precise import of these encapsuled sporular elements 

 has not yet been determined ; but from the proportionate size of their investing 

 sporocysts it may be consistently predicated that they were primarily derived through 

 the conjugation or genetic union of two or more ordinary zooids, while their encap- 

 suled state would seem further to denote that surviving the disintegration of the 

 parent colonies, and probably the drying up of the water with the summer drought, 

 they secure the permanent preservation of the species. 



With reference to the retention and development of the larger and naked 

 sporular elements of Uroglena within the common gelatinous matrix of the parent 

 colony, the similarity of the phenomena to what obtains among the co-ordinate 

 section of the Spongida, and as related at length in a preceding chapter, is at once 

 made manifest. Additional testimony in this direction has to be recorded. The 

 author has on several occasions observed within the parent colonies the presence 

 of smaller spheroidal aggregations, apparently corresponding with the " daughter- 

 spheres" of Volvox or Eudorina, but which, in the event of further corrobora- 

 tion, may be found to possess a still more important significance. These are, in 

 fact, directly comparable with the ciliated gemmules or so-called ciliated larvae 

 of the sponges as they occur in their simplest state, and consist in a like manner 

 of a vesicular moruloid structure, built up of a single stratum of closely approximated 

 flagellate zooids. In a similar way these daughter-spheres of Uroglena provide for the 

 more extensive local dissemination of the species, while the ordinary zooids by simple 

 sporular segmentation contribute towards the enlargement of the parent colony. 

 There can be but little doubt that, as in the case of the daughter-spheres of Volvox 

 and the ciliated gemmules of the Spongida, these corresponding structures in Urogkfia 

 are derived from the primitive coalescence of a considerable number of single cells 

 or zooids. Though this process has not as yet been directly observed, it may be 

 predicated by their occupation of an area towards the periphery corresponding with 

 that normally held by some half a dozen or more of the ordinary animalcules. 



Although a single contractile vesicle only is attributed to the zooids of Uroglena 

 by Biitschli, while such a structure is entirely absent in Stein's latest dehneations of 

 this species, two alternately contracting ones situated towards the centre of one 

 lateral border have been distinctly seen by the present author. Some amount of 

 doubt has hitherto existed as to whether the gelatinous matrix in which the zooids 

 of Uroglena are immersed, is continuous to the centre of the common spheroidal 



