MORPHOLOGY OF CYCLOPS. 21 



which is at other times entirely absent. My silver specimens have not shown the cell- 

 limits. In the living state these membranes have a smeary look. Under certain con- 

 ditions, and especially in young specimens between the moults, and in those specimens 

 which, from their load of epiphytic life, I judge to be aged, they are gorged with oil- 

 globules, especially abundant in the serosa of the back of the stomach. Their colour 

 varies from straw-colour to bright orange, or else is prussian blue. The curious point 

 is the usually symmetrical arrangement of these, a globule of either colour being 

 repeated by a similar one at the opposite side of the middle line. In individuals rich 

 in globules of the yellower shade I have made out an absorption at the purple end of 

 the spectrum, but I have not had access to sufficiently high powers to ascertain whether 

 the globules individually give a distinct absorption spectrum. (The same blue pigment 

 occurs sometimes diffused in thehypoderm, especially about the junction of the segments.) 



The muscles are all well striated, and show typically every line and space enumerated 

 by the histologist. They consist, in the adult, exclusively of contractile substance, and 

 show neither nuclei nor sarcolemma in the adult, though in immature specimens a 

 nucleated mass of protoplasm remains outside the fibre. As mentioned, they may end in 

 the cuticle itself, or be inserted in the parietal connective tissue (muscles of stomach 

 and intestine). In some cases, however, they are inserted by short tendons, into which 

 their fibrillse penetrate a short distance. This is best seen, in the living animal, in the 

 short extensors of the thorax*. 



Ccelomic fluid and Corpuscles. — The ccelomic fluid is colourless ; and, indeed, I have 

 been quite unable to distinguish haemoglobin in any of the tissues. No heart is present 

 in this group t- The corpuscles are amcebiform, richly vacuolated and granular, with 

 fine pseudopodia, by means of which they crawl about ; they may be best seen in the 

 live specimen (supine) in the fourth and fifth thoracic segments, where one rarely fails 

 to see them crawling over the nerve-cord and nerves, without causing any twinges of the 

 muscles. For this reason I gave up my first impression of their being parasitic, and I see 

 that another observer J has found them generally in the Copepoda, and takes the same view 

 of their nature, for which of course he has priority. In preserved and mounted specimens 

 they almost elude observation ; but when found they present 1-3 small rounded nuclei. 

 The circulation of the ccelomic fluid is effected by the digestive system, and will be 

 described below. 



Digestive System (including Respiration and Circulation). 

 The alimentary canal (PL III. figs. 1, 2, 3, 4, 5) begins in a distinct oral cavity bounded 

 by the masticatory limbs and other processes ; from this a narrow gullet rises and ends 

 on the ventral anterior end of the stomach, which is continued back as intestine and rectum 

 to the anus. We shall take these in order. 



* So far as I know, these connective-tissue terminations to muscles have been universally denied for the muscles 

 in the Arthropoda. 



t In the Calanidce a heart is present in the dorsal region behind the reproductive gland (i. e. in the first and second 

 thoracic segments). Like that of Cladocera it is an ovoid sac with meridionaUy arranged muscular fibres forming 

 its walls, with a posterior and two lateral venous ostia, and an arterial ostium in front. 



+ Fric Zool. Anzeiger, Jahrg. v. 1882, p. 498, abstracted Journ. Hoy. Microscopical Society, 1SS2, p. 778. 



