274 Miscellaneous. 



a small parcel of shells dredged by him and Mr. Crispo, of his ship, 

 in Bass's Straits. Amongst them I was greatly interested to find a 

 fresh living specimen of the Tngonia acuticostata, which I described 

 some years ago as one of the most abundant of our Miocene Tertiary 

 species in some localities. The discovery that it still lives, although 

 an excessive rarity in our seas (only the one example being known), 

 will be welcomed by conchologists as well as geologists, from the 

 very small number of living species of Trigonia known. This 

 specimen shows, in even greater clearness than the fossil ones, the 

 total distinction of the ribs from those of the hitherto known living 

 species. The nacre of the interior is pearly white. 



I have, &c., 



Feedekick M'Coy. 



0)1 the Reproduction of the Dioecious Volvox. 

 By M. L.-F. Hennegut. 



Only two species of Volvox; are known, Volvox glohator, L. ( V. 

 stellatuSyWax.)^ and Volvox minor, Stein: the former is monoecious 

 ( Volvox monoicus, Cohn) ; that is to say, the male and female 

 elements are united in the same individual ; the second is dioecious 

 (^Volvox dioicvs, Cohn). 



Cohn has just published (Beitrage zur Biologic der Pflanzen, 1875) 

 a new monograph of the Volvox monoicus, in which he describes the 

 reproduction of this species. I have been enabled, on my part, to 

 trace the mode of evolution of the Volvox dioicus, and to observe 

 some facts which have not yet been noticed. 



Each Volvox is a colony (coenobium) formed of small unicellular 

 algse, furnished with vibratile cilia, and regularly disposed in the 

 thickness of the gelatinous wall of a hollow sphere. There are four 

 kinds of ccenobia : — 1. Some consist only of vegetative cells enclosing 

 in their interior young ccenobia, or daughter- colonies, each one 

 originating by the division and multiplication of a vegetative cell ; 

 2. A large number of these ccenobia contain at the same time male- 

 elements, or androgonidia, situated in the thickness of the gelatinous 

 wall ; 3. Others only present with the vegetative cells some andro- 

 gonidia, and do not produce daughter-colonies ; 4. The female 

 ccenobia contain only gynogonidia, or oospheres, placed in the 

 interior of the sphere. 



The androgonidia are formed at the expense of a vegetative cell, 

 which acquires a slightly larger volume than the others and divides 

 into parallel segments. Each of these segments is in the form of an 

 elongated cone : its thickest extremity is green ; the other, trans- 

 parent, i^resents a small red spot and two vibratile cilia. The 

 bundle of antherozoids displays in the antheridium a constant 

 oscillating movement. 



The gynogonidia are, in like manner, produced by the differentia- 

 tion of a vegetative cell. This becomes much more voluminous than 

 the androgonidia, and filled with a large quantity of starch and 

 chlorophyl granules, which give to the oosphere thus formed a deep- 

 green appearance. 



