24 CCELOMODUCTS IN ARTHROPODA 



A step precedent to the development of the theory of Phlebce- 

 desis was the recognition of the fact that the green glands and 

 " shell glands " of Crustacea, the coxal glands of Limulus and 

 Scorpio, and the generative ducts of Arthropoda generally, belong 

 to that same system of ccelomic exits or ducts to which the renal 

 organs of Mollusca belong. To these we now give the name 

 " urocoels " and " coelomoducts " (see below as to this nomen- 

 clature), and distinguish them from the true nephridia of the 

 Earthworms and Platyhelmia, though they were until quite 

 recently all spoken of by the one term "nephridia." Various 

 anatomists have contributed to the establishment of the fact that 

 the tubular glands at the base of the antennae in Crustacea are 

 connected internally with a frequently very extensive cavity quite 

 distinct from the blood space (Marchal, Comptes Kendus, cxi. 12, 

 and cxi. 16 ; and Weldon, Quart. Jour. Micr. Sci. vol. xxxii. 1891, 

 p. 279 ; and Journ. Mar. Biol. Assoc. vol. i., New Series, 1889-90). 

 The gonadial sacs of Arthropoda, like the gonadial sacs of Mollusca, 

 must be regarded as representing a portion of the coelom, and the 

 cavity into which the other similarly placed ducts open is also in 

 all probability coelom. The blood system need not, therefore (I 

 argued), be considered as in any way representing ccelom ; it is 

 probably only a dilated swollen blood-vascular system which has 

 " crowded out " a good deal of the pre-existing ccelomic chamber 

 or chambers. In 1885 I had arrived at these views, and indicated 

 them in a note to a paper by my pupil, Dr. Gulland, " On the 

 Development of the Coxal Gland of Limulus" (Quart. Jour, of 

 Micros. Sci. 1885, p. 515). At this time Mr. Adam Sedgwick, of 

 Cambridge, was working at the later stages in the development 

 of Peripatus, and early in 1887 announced to the Cambridge 

 Philosophical Society a discovery of the utmost importance in 

 regard to the whole question of the relation of ccelom and vascular 

 system in the Arthropoda. Mr. Sedgwick showed that the coelom 

 of Peripatus capensis is developed as a series of paired cavities in 

 the mesoblastic somites derived from the wall of the archenteron. 

 These paired ccelomic cavities and the axial metenteric cavity are 

 at one time the only spaces to be observed in a transverse section 

 of Peripatus (Fig. 13, A}. The paired ccelomic cavities proceed 

 to divide each into a dorsal and a ventral portion (Fig. 13, C). 

 The dorsal portions form the perigonadial coelom, whilst the 

 ventral portions give rise to the renal tubes and end sacs 

 (epinephric coelom), which have hitherto been spoken of by Balfour, 

 Sedgwick, myself, and others as nephridia, but should no longer be 

 identified with the excretory tubes of Oligochaeta and Platy- 

 helmia, to which the name " nephridium " was originally applied 

 by me, and for which alone it should be reserved. The renal 

 ccelomic tubes of Peripatus must be classed as "uroccels," pro- 



