Miscellaneous. 439 



fice to say that, according to the abstract which I have made of 

 the account (probably incomplete) he kept of the arrivals, he caused 

 to be removed from Rodriguez more than ,'j<i,000 land-tortoises in 

 less than eighteen months. When we reflect on the small extent of 

 the island, we cannot be surprised that thc.so animals, formerly so 

 common, have entirely disappeared ; notwithstanding their fecun- 

 dity, they could not withstand such means of destruction. 



That which wc have stated concerning the tortoises must have taken 

 place also with the land-birds. It is evident that the sailors would 

 not abstain from pursuing and killing them. Those species whose 

 undeveloped wings rendered them easy to capture, while the delicacy 

 of their flesh made them sought after, must have been rapidly exter- 

 minated. It is therefore unnecessary, in order to account for their 

 extinction, to invoke changes in the biological conditions ; the action 

 of man was amply sufficient, and was exerted there without impedi- 

 ment and with more facility than anywhere else. It is still going 

 on in many other parts of the globe ; and we can already foresee 

 the period when many wingless birds, large Cetacea, and certain 

 species of seals and otaries will have been annihilated by man. 

 — Comptes Rendus de V Academic des Sciences, May 10, 1875. 



On the Development of the Pteropoda. By M. H. Fol. 



The vitellus of the Pteropoda before fecundation is histologically 

 a simple cell with a deposit of nutritive matter in its interior. This 

 fecundated vitellus is destitute of membrane and nucleus. It is 

 composed of a formative or protoplasmic portion and of a nutritive 

 portion composed of a network of protoplasm, in the meshes of 

 which the nutritive globules occur. In the centre of the formative 

 part there is a star formed by the granules of the protoplasm ar- 

 ranged in diverging straight lines. The rays of this star stretch to 

 the limit of the formative portion ; and the nutritive globules arrange 

 themselves in lines. 



After the egress of the so-called corpuscle of direction, a nucleus 

 appears in the centre of the star, which is effaced in proportion to 

 the growth of this nucleus. The granules and the globules of 

 the vitellus cease to be in lines. I3efore each segmentation the 

 nucleus disappears, to be replaced by two molecular stars which ori- 

 ginate in its interior. The centre of each of these stars may be 

 regarded as a centre of attraction ; and all the vitelline substance 

 obeys this attraction. After segmentation, a nucleus reappears in 

 the middle of each star, and the \-itellinc substance remains at rest. 



The result of segmentation, which differs little from the recog- 

 nized types of the Gasteropods, is the development of a nutritive 

 portion, composed of three large spheres, and of a formative moiety, of 

 transparent spherules. Afterwards the nutritive cells divide, pro- 

 ducing a superficial layer of little cells, which in the end envelop the 

 three large nutritive spheres and constitute the ectoderm. The 

 fourth of the large central spheres, entirely composed of protoplasm 

 divides completely and causes a thickening of the ectodermic laver. 

 This region corresponds to the lower extremity of the larva. The 

 line of junction of the three nutritive spherules coincides with the oral- 



