180 



CRUSTACEA. 



of this urinary organ was far more complicated than is generally believed. It 

 had been thought probable, from investigation of Peripatus, that the " end-sac " 

 of the anteimal gland might be considered as the vestige of the coelomic sac 

 of this segment. But WELDON found in Palaemon a large coelomic sac lying 

 in front of the genital glands and not communicating with the rest of the 

 body-cavity, but connected with two nephridial canals running forward to 

 the right and left ; these last widened out to form the urinary bladder. To 

 this canal system, the "end-sac," which may be compared with the Malpighian 

 glomerulus, is a lateral addition connected with the urinary bladder by five 

 glandular tubes. As the relations of the body-cavity in the Crustacea are still 

 far from clear, further investigation of this remarkable condition is very 

 desirable. In the meantime, it is perhaps advisable to adhere to the views 

 put forward by GROBBEN. 



That the above pairs of glands and the parts of the mid-gut participating 

 in the formation of the excretory products (in Copepoda and Amphipoda) are 

 by no means the only excretory organs of the Crustacea is proved by the 

 experiments of METSCHNIKOFF and KOWALEVSKY (Biol. Centralbl., Bd. ix.) 

 mentioned above. These authors, by means of coloured injections, demon- 

 strated the presence of small tubes in the thoracic limbs of Mysis, in which 

 the colouring matter accumulated, and of cell-groups in a corresponding position 

 in Nebalia. 



LEBEDINSKY (No. 57) has described the development, in EripMa spinifrons, 

 of a "segmental organ," arising as a paired outgrowth of the somatopleura. 

 The tube thus produced lengthens out anteriorly and forms a coiled canal, 

 which enters into communication with an ectodermal invagination in the coxal 

 joint of the first pair of maxillipedes. 



I. Genital Organs. 



Our knowledge of the development of the genital organs in the 

 Crustacea is as yet very fragmentary. The rudiments of the genital 

 glands belong in all cases to the mesoderm. GROBBEN (No 21) 

 found that, in Cetochilus, the genital rudiments are paired in the 

 Nauplius stage, and lie ventrally to the intestinal canal. Only later 

 do they shift dorsally to a position above the intestine, where they 

 unite to form a single gland. Each of the genital rudiments consists 

 of a large special genital cell, and of adjoining mesoderm-cells which 

 yield the envelopes and efferent ducts.* 



In Moina,-\- probably in connection with its paedo-parthenogenesis, the genital 

 rudiments can be recognised as unpaired genital cells as early as the time when 



* [HACKER (Arcliiv. f. mikr. Anat., Bd. xlix., p. 35 ; "Die Keimbahn von 

 Cyclops") traces the rudiment of the genital gland to a single cell, which is 

 completely isolated at the thirty-two-celled stage, and which can be identified 

 from the first cleavage which divides the egg into two cells, one of which is 

 purely somatic, while the other (the " Kornchenzelle ") gives rise to a certain 

 number of blastomeres (three), but always retains its individuality, and finally 

 divides into the primitive entoderm and the primitive genital cell. ED. ] 



f In Daphnia similis, LEBEDINSKY (No. lla) was unable to distinguish the 

 genital cells at as early a stage as is possible in Moina. Even in the Nauplius 

 stage, the genital rudiments were indistinguishable. 



