C08 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Orientation of Sacculina carcini.* — M. A. Giard deals with sonic 

 criticisms of M. Yves Delage. M. Giard has urged that Sacculina 

 carcini can only be explained on the theory of modified descent, by 

 supposing that the parasite of the symmetrical crab is derived from 

 a Pcltogastcr parasitic on an anomnrous form with twisted tail, 

 which was the ancestor of the Paguridre. In answer to M. Delago' s 

 objection that it is impossible to accept the theory of the derivation 

 of the Brachyura from the Paguridre, it is answered that all that is 

 necessary is to show that the Paguridffl have given rise to certain crabs 

 with a symmetrical abdomen ; this has boon demonstrated by Boas, 

 who has shown that Lithodes is really descended from Eapagurus, and 

 Birgus from Camobita and the Pagurida). 



Against the explanation offered by Delago that the movement of 

 rotation which sets the axis of the Sacculina perpendicular to that of 

 the crab is due to the right receiving more nourishment than the left 

 side, it is sufficient to cite the case of Sacculina bencdeni, which 

 attaches itself to Grapsus ; in this crab the unpaired caicuin opens 

 from below the point where the Sacculina is ordinarily found, and yet 

 the parasite presents just the same characters as in Carcinus msenas. 

 As to the term to be applied to these parasites, no organ of the 

 Sacculina, except the roots, can be properly said to bo internal ; the 

 epithet is good for a certain time, from the topographical point of 

 view, but it is not exact as a morphological application. The method 

 of teasing out the intestine of tho crab is too coarse, ami has led M. 

 Delage into error. 



M. Y. Delago resents f M. Giard's criticism, but no new facts are 

 contributed. 



Vermes. 



Generative Organs of Earthworms.^ — In all the species of Lum- 

 bricus examined by Dr. R. S. Bergh the gonads were found to be in 

 the segments described by Hering. They agree in structure, but the 

 testes vary in form in various species more than the ovary does. The 

 gonads appear during the last period within the cocoon, and have at 

 first the same appearance and structure. Arising as club-shaped 

 thickenings of the peritoneum, they very early become differentiated 

 into a thin epithelial cortex (peritoneum) and an internal mass of 

 primitive germinal cells with peculiar large nuclei. 



With regard to the anatomical relation of the seminal vesicles tho 

 species of Lumbricus fall into two groups, which appear to harmonizo 

 well with the divisions which have been instituted by systematists. 

 In L. terrestris there is a median unpaired vesicle in the ninth and 

 tenth segments, which invests the testes, seminal infundibula, and 

 ventral chain. With this there are connected three pairs of appendages, 

 which lie in the eighth, tenth, and eleventh segments. A similar 

 arrangement is found in L. purpureas, and, according to Hering, in 

 L. rubellus. In other species (L. fcetidus, L. riparius, L. turgidus, 

 L. mticosus), there is no indication of an unpaired median vesicle, bat 



* Comptes Rendus, cii. (1886) pp. 1082-5. f Ibid, PP- 1336-8. 



X Zool. Anzcig., ix. (1886) pp. 231-5. 



