562 SUMMARY OF GUKBENT RESEARCHES RELATING TO 



The arrangement of the nerve-cells in the ganglia of the ganglionic 

 cord, as well as the double nature of the commissures which unite 

 them, prove that the chain has arisen phylogenetically from two lateral 

 nerve-cords. The whole nervous system of Tanais has a greater 

 resemblance to that of the Isopoda than of the Amphipoda ; the 

 reasons for this statement are fully given. 



After many vain inquiries the author was at last able to observe 

 in a young specimen the presence in the auditory vesicle of very fine 

 and very short hairs, which were arranged in a single row on a small 

 part of its inner surface ; no nerve could, however, be detected. Only 

 twelve crystalline cones were found in the eye, and these were very 

 short, and all of the same dimensions. 



The muscles of the body and the appendages were arranged in 

 the manner usual among the Isopoda. The fatty body completely 

 surrounds both the dorsal and ventral faces of the intestine ; below it 

 also surrounds the ventral ganglionic chain and forms the so-called 

 external neurilemma. In the abdomen, where it is most abundant, it 

 forms two large masses on either side of the intestine. It seems to be 

 more abundant in young than in old animals; in old specimens it 

 disappears altogether, so that it seems to play an important part in 

 the nutrient functions of the animal, and in the development of the 

 body and its organs. The adult males take no food. 



Eespiration, in addition to being performed in the manner common 

 among Decapods, is, as in Isopods, also abdominal. After a full 

 description of the anatomy and physiology of the circulatory organs 

 and of the digestive apparatus, in the course of which it is pointed out 

 that the masticating stomach of the female is more complicated than 

 that of the male, Blanc passes to the renal organs ; the seat of the 

 urinary secretion is the fatty body, and the products of secretion are 

 deposited more or less largely along the intestine ; they are yellowish 

 in colour and have the form of agglomerated masses of small rounded 

 or angular corpuscles. Chemical investigations have demonstrated 

 the uric nature of their deposits, and observation has shown that they 

 are more abundant in old than in young examples. 



After some observations, not so complete as the author wished, on 

 the sexual organs and on the " biology " of Tanais, Blanc discusses 

 the question of whether they are Amphipods or Isopods ; the balance 

 of evidence seemed to him to be in favour of the latter, and to justify 

 Milne-Edwards' establishment of a group of " Asellotes heteropodes." 

 As to whether Tanais is the ancestral form of the Isopods, as some 

 have thought, it is necessary to be very careful, but, at the same time, 

 one cannot fail to see such resemblances between Tanais and the 

 zoea-stage of Decapods as is represented by the mode of branchial 

 respiration, the absence of abdominal appendages in the embryonic 

 Tanais, and the possession of eyes placed on short stalks, and of an 

 auditory vesicle which is open to the exterior. 



New and Rare French Crustacea.* — In his 33rd article under 

 this title M. Hesse deals with several new parasitic Crustacea 



* Ann. Soi. Nat.— Zool., xv. (1883) art. No. 3, 48 pp. (3 pie.). 



