322 Miscellaneous. 



fore here bilobecl and, as it were, composed of two ovules placed side 

 by side and similar in form and organization. 



To this first phase others soon succeed which reveal to us the 

 function which these two vesicles are destined to fulfil. Each of 

 these vesicles soon becomes enveloped by fine globules, which make 

 their appearance successively. But whilst round one of them the 

 globules remain very small, retain nearly the same volume through- 

 out, and seem to have a limited multiplication, round the other ve- 

 sicle they present themselves of very different sizes, gradually in- 

 crease, and become more and more abundant as the ovule approaches 

 maturity. 



That lobe of the ovum in which this increase in the number and 

 volume of the primitive elements takes place necessarily undergoes 

 proportionate modifications ; it enlarges for the reception of the 

 materials which increase in it, just as the vitelline membrane of the 

 bird's egg enlarges in proportion as the vitellus is formed, and it 

 finally acquires such a predominance that the other lobe, the deve- 

 lopment of which has remained in a manner stationary, only forms at 

 one of the poles of the ovule a little prominence like that which is 

 produced in the ovum of osseous fishes in consequence of the conden- 

 sation of the vitellus. 



Such is the appearance presented by the mature ovule of the Sac- 

 culince. As to its organization, it only differs from the very small 

 ovules by the intervention in unequal proportions of two distinct 

 elements. The predominant element, formed by a mass of large and 

 small globules, in the midst of which one of the primitive vesicles 

 always shows itself, is, there is no doubt, the analogue of the yelk of 

 the bird's egg — that is to say, the material destined for the nourish- 

 ment of the future embryo ; whilst the restricted disk, situated on 

 the periphery of the ovum and composed of very small granules 

 grouped round the other primitive vesicle, evidently represents the 

 cicatricula of birds — that is to say, the essential and fundamental 

 portion of the ovum, of which the materials are directly employed 

 in the formation of the new creature. 



The study of the ovule of the Sacculince, therefore, gives us the 

 signification of the two vesicles which are contained in the ova of 

 certain species ; we may even say that in this case the demonstration 

 is complete, for we may follow the phenomenon in all its phases. 

 One of these vesicles is the formative centre of the germinative ele- 

 ment, and must retain the name of germinal vesicle under which it is 

 already known ; the other is merely the formative centre of the nu- 

 tritive element. — Comptes Rendus, February 22, 1869, tome lxviii. 

 pp. 460-462. 



Euplectella. 



Dr. C. Claus, the Professor of Zoology and Director of the Zoologi- 

 cal and Zootomical Institute of Marburg, has published an essay on 

 Euplectella aspergillum in quarto, with a beautiful photographic illus- 

 tration representing two varieties of this sponge, and three copper- 

 plates of the spicules of which it is formed. Dr. Claus states that the 



