GRUSTAGEA—EXGEETORY ORGANS 



369 



being intracellular. In the higher Crustacea, however, the cells appear 

 in greater number and more closely crowded, the lumen being 

 intercellular. The urinary canal 

 is very long in the Malacostraca, 

 and lies in complicated coils. At 

 its distal end (near the opening) 

 it widens into the ui'inary bladder. 

 The terminal sac, as well as the 

 urinary canal, may be further 

 complicated in the higher Crusta- 

 ceans by the formation of lateral 

 invaginations. 



The shell gland has essen- 

 tially the same structure as the 



antennal gland. 



That we have to do in the 

 antennal and shell glands with 

 excretory organs is sho^^Ti by the 

 fact that when the animals are 

 fed with carmine, carmine par- 

 ticles are after a time met with 

 in the glandular sacs, at least in 

 those of the antennal glands. 



According to observations 

 made on the Cladocera, the shell 

 glands are said to be of meso- 

 dermal origin. The antennal Fig. 246.— Left Antennal Glana of Mysis 

 glands (of the Cray-fish), on the ^^'f'"'' ^robben). re, Urinary canal; M, urinary 

 ° ^ . , '^ "^ ' . bladder; es, terminal sac; her, blood lacunee ; ea, 



contrary, are said to come from urinary passage (efferent duct). 



a dermal depression, and so 



belong to the dermal glands. These statements, however, require 



further confirmation. 



Morphological Importance. — Leaving out of consideration the different origins 

 mentioned above attributed to these glands it appears probable, from their essential 

 agreement in structure, that the shell and antennal glands are segmental homologous 

 formations. From their wide distribution in the Entomostraca and Malacostraca 

 or their larvae, we may further conclude that these glands are, phylogenetically, 

 very ancient organs, derived from the racial forms of the Crustacea. The view tha-t 

 they are homologous with the nephridia of the Annulata may be supported by many 

 facts in their coarser and finer structure. This view would gain greatly in probability 

 if it could be shown that both are developed out of the mesoderm. This homology 

 has not, however, yet been established. 



This is, perhaps, the place to mention the cement glands of the Cirripedia, 

 which emerge on the last joint but one of the small adhering antennte (anterior 

 antennfe). The hardening secretion of these glands serves to attach the animal to 

 the surface on which it rests. 



Besides these, certain glandular tubes of the Cirripedia, which emerge on the 

 outer maxillae and were formerly taken for olfactory organs, have recently been 

 VOL. I 2 B 



