152 Miscellaneous. 



mussel-culture, besides indicating the importance of such 

 organisms in regard to the nourishment of young food- 

 fishes. The increase of mussels on the rocks at the exit of 

 the main sewage-pipe of the city is also a feature of moment 

 which will subsequently be examined. 



MISCELLANEOUS. 



On the Development of the Chelifers. By J. Barrois. 



The development of the Chelifers differs from that of the other 

 Arachnida by the existence of a larval state which is still hut little 

 known, and which Metschnikoff has described as presenting — (1) 

 externally a muscular lip, two pairs of limbs, and a rudimentary 

 abdomen ; and (2) internally a mass of nutritive vitellus. My 

 researches have led me to recognize a more complex structure. 



The number of pairs of limbs is really five. All the future pairs 

 already exist except the first, but they are completely unfit for 

 locomotion, and consist only of simple projections of the ectoderm. 



The nutritive vitellus is surrounded by a layer of largo ectodermal 

 cells and preceded by a voluminous suctorial apparatus formed by 

 two adprcssed chitinous plates, which separate from each other 

 under the action of a powerful muscular mass placed in front (the 

 muscular lip of Metschnikoff). This suctorial apparatus opens on 

 the ventral surface between the two large chelae (second pair) by a 

 buccal orifice furnished with a pair of peculiar glands, and very 

 different from the definitive mouth. All this constitutes a digestive 

 apparatus ready to function in the mature larva, and which actually 

 functions in passing the nutritive liquids derived from the maternal 

 organism into the interior of the larva. The latter is therefore a 

 true parasitic organism which lives at the expense of its mother, 

 upon the ventral surface of which it is fixed. 



Later on this suctorial apparatus is destined to be cast off. The 

 mode in which it is got rid of constitutes one of the most character- 

 istic features of the development. 



In the Chelifers the nervous groove, instead of forming a single 

 continuous band, from the head to the tail, as in the other Arthro- 

 poda, consists of two separate bands, one placed in front of, and the 

 other behind, the suctorial organ. Subsequently these bands grow 

 together, passing to meet one another above the suctorial apparatus, 

 which they thus completely surround, pressing it downwards ; they 

 thus gradually exclude it from the body of the embryo. When the 

 two bands are finally united into a single continuous band the cus- 

 torial apparatus is pushed entirely outside ; at last it is attached 

 to the embryo only by a slender cord inserted below the definitive 

 mouth, and falls off at the same time as the larval envelope. — 

 Comptes Benches, December 15, 1884, p. 1082. 



