204 PROCEEDINGfi OF THE NATIONAL MUSEUM. vol.39. 



nourishment during the first copepodid stage. Such a condition 

 must be kept clearly in mind since it will profoundly influence our 

 interpretation of the free-swimming period. 



The extremely rudimentary eye (e) can now be distinguished inside 

 the coils of the attachment filament. It is made up of three ovate 

 ocelli, two dorso-lateral and one inferomedian, which are entirely 

 separated from one another and devoid of pigment. The structure 

 of each ocellus has also degenerated until all that remains is a more 

 or less granular mass, staining deeply in hsematoxylin and containing 

 near its anterior end three lighter spots. No trace of lenses can be 

 found in any of the sections and the entire structure disappears 

 during the next stage. 



Attachment filament. — By far the most interesting structure in the 

 body of this fused larva remains to be described. This is the attach- 

 ment filament, already mentioned, which can be seen close to the 

 dorsal surface of the body beneath the patch of bro\\Ti pigment 

 (fig. 10). It is of interest not only by reason of its intrinsic anatomy, 

 which is very peculiar, but also on account of the function which it 

 subsequently performs. It is an organ which in other parasitic 

 copepods appears at a much later stage, but has here been shifted 

 back to the very beginning of larval development. 



It also differs radically from all other attachment devices and is 

 admirably suited to the complicated function it has to perform. In 

 the Caligida3 the filament is manufactured during the process of 

 attachment out of the viscid secretion of a gland, which hardens 

 when it strikes the water. Previous to attachment the larva swims 

 about freely. 



In the present species the filament is of solid tissue and is formed 

 slowly inside the body of the larva during the long period it passes 

 within the egg. It is fully developed before the larva is hatched, 

 which is a strong indication that the free-swimming period is to be 

 very short, and we find this fully realized. Furthermore in the 

 Caligidse the larva is only attached through two or three moults and 

 then becomes free-swimming again. In our Achtheres larva the first 

 attachment is maintained by the female throughout life and by the 

 male up to the time of complete sexual development. 



The organ of attachment consists of a long filament coiled up like 

 a rope, the two ends extending forward to the frontal margin and 

 considerably enlarged. The ends and the straight portion in front 

 of the coil are surrounded by a large mass of glandular tissue which 

 evidently secretes the filament (fig. 13). The development of this 

 organ is as follows: There appears first very early in the nauplius 

 stage an oval mass of glandular cells (fg., fig. 12) on the midline, close 

 to the frontal margin. This is the frontal gland and corresponds 

 with the one which appears in the chalimus larva of the Caligidae. 



