132 REVIEWS. 



MysidfiD. Tlie development of the embryo in this abnormal family 

 had already been shortly described, but Professor Van Beneden has 

 here worked it out in detail, and has pointed out several interesting 

 facts in addition to those already knowTi. 



The MysidiB have no true branchiae ; but in connection with the 

 heart there are, on each side, five small lateral blood-vessels, and 

 according to Professor Van Beneden, " Ces canaux correspondent 

 " exactement aux vaisseaux brauchiaux des crustaces plus eleves, et 

 " e'est sur leur trajet que se developpent les lamelles branchiales des 

 " decapodes en general. II existe ainsi une petite circulation ; le 

 " sang sort du coeur et, apres avoir, parcouru la place qu'occupent 

 " les brancliies dans les autres decapodes et surtout apres avoir regu 

 " un confluent veineux des appendices cephaliques, retoiu-ne rapide- 

 " ment au meme coeur pour en etre chasse de nouveau." Professor 

 Van Beneden considers that Mysis difters from the other Crustacea 

 in the curvature of the body of the embryo. " II est inutile," he says, 

 " de faire remarquer que les Mysis s'eloignent des crustaces, tant par 

 " les premiers rudiments de Tapparition blastodermique que par la 

 " maniere dont le corps se replie sur lui meme. En general I'abdomen 

 " et la queue se plieut sous le thorax et se croisent avec les appendices 

 " cephalothoraciques. Dans les Mysis, le corps se replie en sens 

 " inverse vers le dos, et tous les aj^pendices, depuis ceux de la tete 

 " jusqu'a ceux dela queue, au lieu de secroiser, sont couches dans le 

 " meme sens." Not only, however, is this the case, as he admits in 

 the allied genera Idothea and Ligia, but we find the same thing also 

 in Oniscus and Asellus (Rathke Abhandlungen zur bildungs- und 

 entwickelungs — Geschichte des menschen und der Tliiere. Leipsig, 

 1832-1833). And it is also well shown in Zaddach's beautiful 

 memoir on the embryology of Phryganea (Untersuchungen liber die 

 Entwickelung und den Ban der Grliederthiere. Berlin, 1854). In 

 the Diptera and Coleoptera, namely in Donacia crassipes among 

 beetles, in Chironomus,* Simvilia (see Kolliker's " Observationes de 

 prima inscctorum genesi"), and Melophagus (Die Portpflanzung und 

 Entwickelung der Pupiparen, Leuckart), among flies, the same 

 phenomenon holds good; so that far from regarding it as exceptional 

 and peculiar to Mysis, we are rather disposed to look upon it as the 

 normal disposition of the embryo among the Articulata. 



The condition and embryonic development of the organs of sensa- 

 tion in Mysis are especially interesting. With reference to the ocular 

 peduncles, indeed. Professor Van Beneden says, p. 62, " Ce pedicule 

 " (le pedicule oculaire) n' apparait aucunement comme les autres appen- 

 " dices,et semble avoir une autre valeur morphologique ; " an assertion, 

 however, which appears scarcely reconcileable with his, almost imme- 



* With reference to Chironomus, Kollikcr expressly says : — " Qiiando primum 

 " corporis articuhvtio expressa cerni jiotost, primus ad octavum us(pic articuhim in 

 " parte abdoniinah, nonus ad tertium dccimum in ori dorso siti huut" — a position 

 which is well shown in the plate. 



