REPORT ON THE CIRRIPEDIA. 5 



a. Description and Comparison op Cypris-Larv^e. 



At first I experienced great difficulties in identifying the parts of the body of the 

 complemental male ; however, I believe I have solved the problem by comparing the 

 full-grown male with a younger stage of its development, and the latter with the 

 corresponding stage of an ordinary species of Lepas. The occurrence of a Cypris-larva 

 between the two complemental males at the ordinary place enabled me to make this 

 comparison ; from its structure as well as from the place whence it was taken there can 

 be no doubt, I believe, that this latter creature was destined to develop (retro- 

 gressively of course) into a complemental male. 



The species of Lepas, the Cypris-larvge of which have served me for comparison, was 

 the Lepas australis, Darwin. It is not only very characteristic on account of its great 

 size, but it is also the best known Cypris-larva, as it served first for the investigations of 

 Darwin, and again some years ago for the studies of Claus. The latter has given a very good 

 figure of the internal structure of this larva as seen in a sagittal section. My figs. 

 1 and 2 on PI. II. very closely correspond to that of Claus. My fig. 1 was drawn from a 

 preparation made by dividing the body of the Cypris-larva of Lepas australis into two 

 nearly equal halves by means of a sagittal section. The rounded spot (A M) is the 

 adductor muscle of the two valves of the Cypris-larva ; the straight line at the under 

 side of the valve represents the ventral side, the convex one the dorsal side ; the 

 extremity on the left of my figure the frontal (cephalic), the one facing it the hinder 

 (abdominal) extremity of the body ; from the way in which the spines of the legs are 

 stretched out at the ventral side it is clear that there is a slit-like opening between the 

 adductor muscle and the hinder extremity of the body. In fig. 2 of PI. I., 

 representing a longitudinal section parallel to and at a little distance from the ventral 

 margin, this orifice is also distinct. This is the only place where the interior of the sack 

 or mantle (as Darwin calls it) is in open communication with the surrounding water. 



The body of the future Lepas is enclosed within the sack and has also a wall of its 

 own ; on one side (the right hand side of the figure) this wall is very distinct, and it 

 passes over near the middle of the dorsal margin into a transverse invagination which 

 almost reaches up to the ventral side. It is by this invagination that the division of the 

 body into a capitulum and a peduncle is brought about ; what in fig. 1 of PL II. is 

 placed on the right hand side of the invagination (Inv.) is the capitulum, what is placed 

 on the left hand side the peduncle. As the invagination of the dorsal wall does not reach 

 as far as the ventral side, a direct communication remains between the capitulum and the 

 peduncle. Through this commissure, which is very narrow in the full-grown animal, pass 

 the oviducts and the nerves destined for the peduncle. 



On the ventral side an invagination is seen at a distance of about one-fourth of the 

 total length from the peduncular extremity ; at the bottom of this invagination, when 



