34 PROF. M. M. HAETOG ON THE 



right and left from its centre, of whose real nature I am in doubt, though it is natural 

 to compare them to the muscular slips which move the eye of Diaptomus, which would 

 lose their muscular character in an immovable eye like that of Cyclops. The median 

 eye looks directly down on the rostrum, which probably serves as a cornea. The lateral 

 ocelli are much more flattened and contain more bacilli — at least eight to ten peripheral 

 and three central. They face outwards and forwards. In front of each is a nearly 

 circular corneal facet, forming a slight depression in the frontal region, where it escapes 

 notice in almost every view, being best seen in a dissection of the fresh animal treated 

 with ammonia *. In the inner limb of each bacillus is an 'oblong body (probably a 

 rliabdome), staining deeply with osmic acid, hsematoxylin, &c. 



This account is not so satisfactory as I could wish, owing to the extreme difficulty of 

 dissecting out and treating under the cover so minute an organ ; while in imbedding, 

 cutting and clearing, shrinkages take place ; and a natural anxiety as the razor 

 approaches the important place often spoils the median section. Not one in ten of my 

 series shows the eye satisfactorily. But all the above points are clearly made out. 



In both Cyclops and Calanus I have traced a few fibres along the septum, between 

 the blocks of the lateral ocelli. That they do not enter the bacilli I am positive ; I 

 believe they pass on to the frontal region, or ends in the nuclei of the blocks. The strongest 

 confirmation of this view is to be found in the structure of the eyes of CoryeEeidse and 

 Pontellidae. 



Reproductive System. 



The reproductive organs consist in both sexes of a median egg-shajjed reproductive 

 gland, situated in the tergal region of the first thoracic segment (i. e. under the hinder 

 part of the carapace), with its pointed " embryonic " t part posterior, and sometimes bent 

 down and forwards, and giving off at its wide anterior end two ducts, which turn down- 

 wards and backwards to end, each under a genital valve, in the fifth thoracic segment. 

 In both sexes the gland, though supported by a sort of mesentery, can scarcely be said 

 to have a proper investment. The first origin of the gland is by two large nucleated cells J, 



* From the difficulty of finding these corneas under ordinary conditions they have been noticed by Claus alone 

 in Cyclops tenuicornis (Freil. Cop. p. 45, Taf. ii. fig. 17). They probably exist throughout the genus. Grenacher 

 describes the eye of Calanella very differently (Sehorg. d. Arthropoden, p. 63, Taf. v. fig. 36, Taf. vi. figs. 37, 38). 

 He describes central cells, -which are evidently part of what I term the blocks ; he also figures the nerve-fibres as 

 entering on the proximal side of the bacilli, stating that he has followed them certainly, though with extreme 

 difficulty. I havo examined the eye of Calanus in old spirit-specimens, which, however, were in fair condition, both 

 by dissections and sections ; this evidently is on the same type as that of Calanella, differing from Cyclops in the fact 

 of the blocks not extending backwards, so that they leave a space at their hinder end, into which the optic ucrve 

 enters before breaking up into a ventral and two lateral branches. I cannot speak positively as to the ventral 

 branch. The lateral branches unquestionably do not enter the inner ends of the bacilli. A discussion as to the 

 morphological importance of this eye will be found in the concluding section " On the Systematic Position of the 

 Copepoda." 



t Gruber's paper (see ante, p. 1, note) revolutionized our knowledge of these organs in the Copepoda. It has 

 been a most valuable guide to me. 



X I find that FriS has anticipated me in this (Zool. Anz. 1882). 



