22 MICROSCOPICAL STUDIES. 



With such definition Monstrilla closely agrees if the italicized 

 part be omitted. Every vestige of the usually well developed and 

 complicated mouth organs is absent ; the posterior antenna) have shared 

 a like fate, and further, no trace of alimentary canal can be made 

 out, though a very short tubular proboscis is apparent. This however 

 leads nowhere, and I am inclined to hazard the suggestion that these 

 animals may live during the greater part of life as suctorial parasites 

 upon or within some larger animal, but that at breeding time (Aug. 

 and Sept.) they leave their hosts and seek for mates, free-swimming 

 in the surface waters of the sea. Certainly many species of copepoda 

 do live as parasites, e.g. the whole family of Notodelphyidse affect some 

 or other of the simple Ascidians, while others live within the cockle, 

 pecten (6) and other shell-fish. Regarding the assumption that 

 MoiiHtrilla forsakes the host at the breeding time, and that stomach 

 and intestine become absorbed coincidently, such would not be 

 without parallel among other animals. Thus those small free- 

 swimming worms, the Syllida?, forsake their homes among the 

 corallines as the time for reproduction approaches, and are found 

 among the surface life of the sea with alimentary canal reduced to a 

 mere cord or else entirely atrophied, and the cavity of the body 

 wholly filled by masses of ova or of sperm. Reference to PI. iv, 

 Fig. 9, will show how the ova in Monstrilla is similarly disposed. 

 Mr. I. 0. Thompson has indeed (5) considered and condemned 

 the view that this animal may be a sucking parasite but apparently 

 he has overlooked the probability now suggested, of its regularly 

 abandoning such habit and altering its anatomy at the breeding 

 season. He adduced the fact that all specimens of Monstrilla have 

 been recorded as free -swimmers near the surface but considering 

 that a copepod, common in, and peculiar to the cockle, was only 

 discovered in 1892, there is plenty of chance of this supposed 

 parasitic habitat of Monstrilla having been overlooked. Hence 

 I cannot without positive evidence agree with Bourne (7) in the 

 possibility that " the adult may be preceded by a predaceous larva 

 supplied with mouth parts and an alimentary tract, which, after a 

 succession of rapid ecdyses, develops into the mature sexual form, 

 whose only function is that of reproduction." But we have no record 

 of such a larva having been seen and as such would be less easily 

 overlooked than would a parasitic adult in some perhaps obscure host, 

 I think the suggestion I mention is the more probable. A great deal 

 of work has yet to be done ere the parasitic copepoda are even fairly 

 well known, arid I would therefore draw the attention of workers 

 to what assuredly is a promising field for research. 



The few appendages possessed by Monstrilla are all exceedingly 

 interesting when viewed under a high power. Thus if we examine 



