On the DevelojimetU of Cirripedia. 159 



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 

 cjeca, 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 or of its nucleolus. 

 Some highly refractive 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. 



7. As soon as the segmentation begins, large transparent cells 

 are seen separating themselves from the yelk-globules, and in- 

 creasing in number as the segmentation goes on. 



8. These cells form a blastoderm round the yelk. No primitive 

 streak could be seen ; but its presence is not denied, as the object 

 is not favourable for these observations. 



9. The blastoderm loses its cellular structure and gives way 

 to a granular skin. On both sides of a longitudinal groove three 

 pairs of appendages begin to be visible. 



10. The test of the ovum extends as the embryo develops. The 

 latter is very likely still enveloped by a thin blastodermic cuticle, 

 which is clearly visible at the ends of the tail and antennae when it 

 comes out. 



11. The development of the Nauplius in the ovum of this Lepas 

 shows very much the same stages as those described by Buchholz 

 in Balanus iynprovisus. 



II. The Nauplius stages. 



1. The NaiipliurS of Lepas fascicidaris has, on leaving the Qgo,, 

 a length of 0-35 millim. It moults at least five times, and 

 has before throwing off for the last time the Nauplial appendages 

 a length of 12 millims. 



2. The first stage of the Nauplius has been seen by Darwin, 

 who describes it, and also by Burmeister. 



3. After the first two moults the Nauplius gets a large dorsal 

 spine and enters a series of stages, one of which has been described 

 in another Lepas by Dohrn as Archizoea gigas. 



4. Reasons are given why Archizoea gigas is nearly certain 

 to be the Nauplius of Lepas australis, a species closely allied to 

 Lepas fasdcularis, and representing it south of the equator. 

 Archizoea gif/as was caught, together with the large Cyprides of 

 Lepas australis, during the ' Challenger's ' antarctic cruise. 



5. The tail and the caudal spine of the newly hatched Nauplius- 



