44 Embryonic development and Larvai Stages. 



Note. — My failure to obtain the Cypris larvae of the Rhizocephala, by rearing the Nauplii, requires some 

 explanation. Delage has given a description of the inethod by whioh he obtained the Cypris, and I have naturally 

 followed his methods with great care, but without success. He found that it was necessary to choose Sacculinae 

 of a purple colour in which the Nauplii were nearly ready to be hatched out, to wait for the emission of the 

 larvae, and then to keep them in a vessel of water without current or aeration. Under favourable circumstances 

 the Nauplii should change into Cypris larvae in four days, and the Cypris should be ready to fix on the Sacculinae 

 at the end of four more days of free existence. The chief source of failure, according to Delage, consists in not 

 obtaining a normal emission of the Nauplii from the brood-pouch of the parent. 



Pollowing Delage's directions I have obtained on more than a hundred occasions the emission of the Nauplii 

 of Saceulìna negleeta, S. bemdeni and Peltogaster curvatus, but although the larvae have been kept alive for as long 

 as seven days they have never changed into Cypris, unhealthy signs being sooner or later always apparent in them. 



The Nauplii of Peltogaster and of Sacculina behave very differently, those of Peltogaster being feebly helio- 

 tropic and strongly negatively geotropic, those of Sacculina beeing strongly heliotropic and without any marked 

 reaction to gravity. The rearing of the Nauplii of Peltogaster, without some special apparatus which has not yet 

 been devised for marine larvae, is really hopeless, as the larvae soon reach the surface film of the water, and the 

 presence of any motion in the water to disturb the surface film is fatai. 



With Sacculina it is easy to keep the Nauplii alive for a long time, and I am unable to state the cause 

 of my failure to obtain the Cypris. I have observed that the Nauplii of Sacculina benedetti live longer than those 

 of S. negleeta, perhaps owing to the host of S. benedeni, viz. Pacliygrapsus marmoratus, being a littoral form and 

 therefore exposed to more varying conditions in a state of nature, but as S. benedeni is not very common at 

 Naples I have not been able to obtain it in sufficient quantities for performing a successful experiment, large quan- 

 tities of material being essential for success, as Delage has repeatedly insisted. The form on which Delage worked 

 was S. carcini, the parasite of Carcinus maenas; and the fact that this race of Sacculina is parasitic on a littoral 

 species of crab and is exceedingly common at Roscoff, may account in some measure for Delage's success. 



List of Literature. 



1. van Beneden, E., Recheiches sur l'embryogénie des Crustacés. Développement de l'oeuf et de l'embryon 



des Sacculines. in: Bull. Acad. Se. Belg. (2) Tome 29 pp. 99 and 599 1870. 



2. Delage, Y., Evolution de la Sacculine, in: Arch. Z. Expér. (2) Tome 2 p. 417 1884. 



3. Abile, P., Les premiers stades du développement de la Sacculine, in: C. R. Acad. Se. Paris Tome 139 



p. 430 1904. 



