1875.] On the Development of Cirripedia. 129 



II. " On the Development of Lepas fascicularis and the ( Archi- 

 zoea' of Cirripedia." By R. von Willemoes-Suhm, Ph.D., 

 Naturalist to the ' Challenger ' Expedition. Communicated 

 by Prof. C. Wyville Thomson, F.R.S. Received September 



28, 1875. 



(Abstract.) 



The materials for this paper were obtained during the ' Challenger's ' 

 cruise from Japan to the Sandwich Islands in 35° lat. N., when very 

 curious Nauplii, some of them 12 millims. long, were caught, which were 

 identified at once as belonging to the nauplial form to which Dohrn has 

 given the generic name of " Archizoea" In the daytime these larvae 

 were scarcer, but at night so common that large bottles could be filled 

 with them. The question (which had been left open by Dohrn) to which 

 cirriped these extraordinary JSauplii might belong was solved when 

 large quantities of Lepas fascicularis were seen passing the ship for more 

 than a week. It was then possible to keep these barnacles alive and to 

 bring up in our globes such stages of the large Nauplii as had also been 

 taken on the surface. Then, again, when catching the surface-animals, 

 free-swimming pupae were found, which were seen to settle on dead 

 Velellce and assume the form of Lepas fascicularis, so that the whole 

 development of this species could be worked out. 



Reasons are given why this barnacle belongs to the species Lepas 

 fascicularis ; and a description is given of some parts of the mouth, which 

 slightly differ from those described by Darwin in the same species. 



I. Development of the egg and of the youngest Nauplius. 



The conclusions to which an investigation into the development of the 

 ovum, and into the changes which occur in it after its formation up to 

 the time when the Nauplius comes out, has led are the following : — 



1. The youngest eggs, seen in the caeca of the ovarian tubes, are 

 transparent cells with nucleus and nucleolus. 



2. The germinal vesicle, as well as the ovum, grows by taking up 

 elements of yelk. 



3. All the ova found in the ovary of a barnacle are in the same stage 

 of development. When mature ova are to be seen in the tube, small 

 undeveloped ova may be seen here and there in the caeca, which act very 

 likely as mother cells for further breeding-purposes. 



4. The spermatozoa, when fully developed, are simple hair-like 

 filaments. 



5. The mature ovum, as contained in the breeding-lamellae, shows no 

 trace of the vesicula germinalis nor of its nucleolus. Some highly re- 

 fractive granules may be seen here and there among the yelk-globules. 

 The ovum is oval in form. 



6. The segmentation is very irregular, but seems to be complete, 



