ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 515 



also begin to appear. Still later on, it may be seen that the septa 

 form three or four cycles, which consist respectively of 12, 12, 24, 

 and 48 pieces; the younger always appear between two older 

 ones. 



Development of iEquorea.* — Prof. C Claus states that JEquorea 

 forsJcolea deposits its ova in March. They are without an investing 

 membrane, and are deposited in great quantities. The directive cor- 

 puscle is soon expelled, and just below the point at which it escaped a 

 clear vesicle may be seen in the yolk for a few hours afterwards. The 

 central cleavage-cavity is open at both ends until the 16-sphere 

 stage. Later on, when these become closed, the region of the upper 

 pole may be still distinguished by the greater thinness of the walls of 

 the hollow sphere at that point. As the cells become smaller, cilia 

 appear on the surface, and the mass begins to rotate. It soon, how- 

 ever, elongates, and becomes narrower near the lower pole, which is 

 now posterior. The cells of this region become much higher, and 

 gradually form a projecting process into the cleavage-cavity. Some of 

 the more internal cells break away, and form isolated spheres within 

 that space. This process goes on until the whole becomes filled with 

 small cells, which represent the endoderm. At first there is distinct 

 continuity between the endodermal cells, and the ectodermal from 

 which they have arisen. On the third day the embryo presents all 

 the characters of a Planula, and swims freely about. Stinging cells 

 appear, and the long axis of the body is marked by a somewhat irre- 

 gular line, which is the optical expression of a cleft in the endoderm. 

 On the fourth and fifth days this cleft becomes wider and filled with 

 dark granules. In this condition the larva swims about freely for 

 some time. Fixation has not been directly observed. 



This polar ingrowth of the endodermal cells is not any kind of 

 delamination, but has, as the author hopes to show in a further 

 communication, a not distant connection with the other mode of 

 development, which is known as that of invagination. 



Porifera. 



Hybridization in Fresh-water Sponges.t — Mr. E. Potts, in ex- 

 hibiting some fragments of fresh-water sponges collected in the 

 Boston Aqueduct, consisting of, it is believed, Spongilla paupercula 

 and a new species, Meyenia acuminata (with others), points out the 

 following exceptional features as marking the collection : (1) that all 

 the statospheres, whether belonging to Spongilla or Meyenia, were 

 smooth, that is, without a granular or cellular "crust"; (2) the 

 apparent absence of dermal spicules in both, and the abnormal 

 character of these belonging to the statospheres. The appearance is 

 not infrequent, but has, so far as known, heretofore been limited to 

 the genus Spongilla. The recurrence of the same feature in the 

 associated genus Meyenia, coupled with the fact that many of the 

 birotulates upon its statospheres were imperfect, the rays being more 



* Zool. Anzeig., v. (1882) pp. 284-7. 



t Proc. Acad. Nat. Sci. Philad., 1882, pp. 69-70. 



2 at 2 



