ZOOLOGY AND BOTANY, MIOBOSCOPY, ETC. 499 



generally known as the egg in Asciclians is not what is ordinarily 

 regarded as such ; it is rather an ooblast which produces eggs, and it is 

 consequently comijarable to the ooblast of the Appendicularia (Fritillaria). 

 The eggs produced by the ooblast function as such in the Appendicularia, 

 while in Ascidiaus only one is capable of fertilization ; all the rest 

 become aborted and may be spoken of as testa-cells. The nuclei of all 

 the eggs arise as buds of the nucleus of the ooblast or karyoblast. In 

 Asciclians they are formed as simple constrictions of parts of the 

 membrane and reticulum of the karyoblast, without the intervention of 

 the nucleolus. On the surface of the ooblast of DistapUa they increase 

 karyokinetically. Later on the muscular buds or uucleogemmee become 

 surrounded by part of the protoplasm of the ooblast ; and thus become 

 cells, and separate from the ooblast. The eggs of the Appendicularia 

 retain, on constriction, a follicular investment, with which the complex 

 of ooblasts of these animals is from the first surrounded. In Ascidians 

 the abortive eggs do not retain any covering, but lie in the space between 

 the egg and the follicular epithelium. 



There is reason to suppose that the reduction of the eggs formed by 

 the ooblast goes still further than is the case in Ascidiaus. The nucleo- 

 gemma3 Icse their specific protoj)lasmic covering and become lost in the 

 ooblast. The various phenomena of formation of buds of the karyoblast 

 which have been several times observed in Vertebrates are probably of 

 the same character. In later stages of cleavage it may be seen that some 

 of the abortive eggs of Distaplia are entirely the large endoblast cells, 

 while others remain for some time without taking any part in forming 

 the tissues of the larva. When the abortive eggs have left the ooblast 

 the latter forms a true egg. All the protoplasm of the egg breaks up 

 into yolk-bodies in such a way that no intermediate substance is retained. 

 At the same time the membrane and reticulum of the germinal vesicle 

 become lost in its karyoplasm and are converted into a plasmatic, 

 actively moving, amoeboid body, which gradually extends itself in a 

 plexiform fashion in the whole egg (ergoplasm). The nucleolus, 

 which has till now remained passive, is converted by internal histo- 

 logical differentiation into a " polar nucleus " with membrane, nuclear 

 network, and nucleolus. By the action of the ergoplasm the polar 

 nucleus is conveyed to the periphery of the egg ; it loses its membrane 

 and network, its chromatin becoming converted into chromatic loops, 

 which give rise to a chromatic figure when the polar globule is con- 

 stricted off. It behaves therefore just as the germinal vesicle is known 

 to do. The formation of one polar globule was observed, and this must 

 be regarded as cell-division. Biitschli's hypothesis that the polar 

 globules are rudimentary eggs is so far supported by what obtains in 

 Distaplia where the abortive eggs are all of the same size after their 

 division. The cleavage nucleus is surrounded by a large quantity of 

 ergoplasm ; when observed it was found to consist of a large number of 

 similar merites. The ergoplasm is to be identified with the protoplasm 

 of Kuppfer. 



p. Bryozoa. 



Anatomy of an Arenaceous Polyzoon.* — Mr. A. Dendy describes a 

 remarkable new genus of ctenostomatous Polyzoa, found near Port Phillip 

 Head, which he calls Criji^tozoon, and of which two species, C. loilsoni and 



* Eoyal Soc. of Victoria, 1889, 8vo, 11 pp. and 3 pis. 



