6(5 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in tbe postlarval period. Moreover, this blastogenesis is centripetal, the 

 new individuals appearing outside the cycle already in activity. An 

 arrangement which frequently obtains may be indicated by the following 

 diagram : — 



It is interesting to note that tlie buds, to whatever stage they belong, 

 are at first hermaphrodite ; in the cold season both glands atrophy as the 

 bud grows; later on, the male gonad alone persists ; in warm weather both 

 kinds of gonads are completely developed, 



j3. Polyzoa, 



Phylogeny and Ontogeny of the Polyzoa.* — Herr K. Krapelin 

 communicates some of the results of a prolonged study of the fresh-water 

 Polyzoa of Germany. 



I. Phylogeny. — The Phylactolaemata are derived from the Ctenostomata, 

 and especially from forms like Arachnidium and Victorella, which possess 

 creeping processes with knotted swellings. From these the Paludicellsa 

 first develope with hibernacula or winter buds, comparable to the tuber- 

 culate swellings of the former. The hibernacula are true buds, with 

 embryos containing ecto- and endoderm, and represent the statoblasts of 

 the Phylactolaemata and especially those of Fredericella, which is not 

 forked like PaludiceUa but bears at the position of the lateral branch an 

 internal statoblast with bivalve shell. The statoblasts of Fredericella are 

 borne both on the creeiiing and on the upright cystids. Fredericella is an 

 important transitional form connecting Phylactolfemata and Ctenostomata. 

 Further development occurs along two lines, («) alteration in the con- 

 sistence of the chitinous ectocyst, and (h) multiplication of the number of 

 tentacles. A development of the lophophore, and increased production of 

 statoblasts, are associated with the resulting improvement of nutritive 

 conditions. Statoblasts with and without swimming ring appear together. 

 With increased firmness of ectocyst vertical cystids preponderate as in 

 Alcyonella, while the reverse I'esults in hyaline creeping forms. The sessile 

 statoblasts disappear, and si)inose anchor-bearing forms with swimming 

 rings replace them, 



II. Ontogeny. — The spermatozoa arise directly from naked " endoderm " 

 speimatides, the head forms the nucleus, and a " residual body " remains. 

 1'he ova also result from " endoderm " cells of the cystid wall, not of the 

 funiculus. They are surrounded by an " endoderm epithelium " and thus 

 form an ovary of the simplest type. They are fertilized in the ovary 

 and do not pass into the body-cavity. 



The segmentation results in a mass of uniform cells. These differentiate 

 into two groups of which one forms the embryo, while the other is apposed 

 to the maternal embryonal envelope and degenerates. A blastula with wide 

 central cavity is formed, and sumo kind of embolic process forms a 

 " gastrula," The gastrula-cavity is the future body-cavity, and its layers 



* Biol. Centralbl., vi. (1886) pp, 509-C02 (Bcr. 59 Versamml. Dcutsch. Naturf. 

 u. Aerzte, Berlin, 1886). 



