16 Mindeskrift tor J. Steenstrup. XVI. 



hosts are provided with an enormous number of this parasite, and why these are to 

 be found of very different age and size. In the latter case the larvæ might most 

 easily make their way out through the bursal slits, and in spite of their lack of eyes 

 they may find without great difficulty new Asteronyx, as these animals cling to the 

 often densely congregated sea-pens. The way leading to the interior of the new hosts, 

 I think again would be the bursal slits. In both cases the larva is supposed to attach 

 itseif by means of its hooked maxillæ, either among the genital sacs of the host, or 

 on that face of its intestinal wall, which looks towards the bursal pouch, or on the 

 inner dorsal body-wall, and the stimulation due to this fixation may cause the tissues 

 to produce a gall. Quite exceptionally the larva may fix itseif on the outer surface 

 of an Asteronyx; this is shown by the few cases of external galls mentioned before. 

 That the larvæ should be able to make their way to the interior of the host by 

 active working through its body wall (f. ex. through the dorsal wall, the inside of 

 which is often studded with parasites), seems to me most improbable. How far the 

 course of things here set forth will prove to be the right one, I hope \sill be tested 

 some day by others, who may have the luck of investigating the living animals 

 in their mutual relations. 



The Cyclops-larva (Fig. 22—23) has a length of 0,304—0,320 mm from the front 

 to the end of the telson (of this the tail takes up only ca. 0,072 mm; the furcai setæ 

 have about the length of the tail). The general shape is that of a Cyclops; the trunk 

 is ovoid, somewhat compressed laterally; the short and slender abdomen is often 

 directed obliquely upwards. The head has a carapace distinctly marked off , with a 

 short, rounded rostrum, curved down between the antennules; the thoracic segments, 

 especially the three last ones, are sharply defined; the belly is arched; hence the body, 

 seen in profile, is rather high. The antennules are strong and — as far as I have 

 made out — composed of seven joints, the outermost one long and transversely cut 

 at the end; each joint is provided on its front side with a seta, some of the basal 

 joints with two setæ; the terminal joints have besides setæ on their back; the 

 ultimate, penultimate and the fourth (from the tip) carry each a large "aesthetasc" (ae) '). 



The antennæ (a,) are short, slender, three-jointed (the outer branch of course is 

 absent); the last joint with two terminal setæ. Mandibles, maxillulæ and eyes are 

 absent. The maxillæ (mx) are very strong, composed of three segments, the terminal 

 a hooked claw. Each of the four thoracic swimming feet (Fig. 24) has a well devel- 

 oped basal stem (b) and two rami (y and i) of unequal length ; as usual in Copepoda 



1) It may be possible that all the larvæ, I have found, are male individuals, although I have 

 found and examined a good many specimens. When I have not been able to make a fuU state- 

 ment regarding the number of joints in the antennules, their number of setæ and the arrangement 

 and length of the latter, the reason is that the segmentation is very feebly pronounced, and that 

 particles of the tissues of the host, obscuring the structures, could not be cleared completely away. 



