410 EDGAR J. ALLEN. 



iu the region of the second maxillae contain the proximal ends 

 of the shell-glands; and fourthly, the cavities of the limbs, 

 which contain the distal ends of the same organs. The 

 cavities of the limbs communicate with the lateral cavities, 

 and the latter frequently communicate with the central cavity 

 by the disappearance of the connective-tissue bands. The 

 three latter cavities all contain blood. The intestine, the 

 liver lobes, the nerve-cord, and the muscles are each sur- 

 rounded by a definite layer of mesoderm. That surrounding 

 the liver is strongly muscular, the lobes in the living larva 

 being often seen to vigorously contract. Around the shell- 

 gland I have been unable to detect any similar mesodermal 

 investment. 



In the parts of the thorax anterior to the region of 

 Maxilla II a similar condition of things occurs (fig. 9), except 

 that the central cavity is somewhat broken up by the masses 

 of muscle which move the mandibles. No trace of nephridia 

 has been seen in the segments between Antenna II and 

 Maxilla II, but a section through the region of the first 

 maxillse (fig. 9) shows in the lateral cavities a single pair of 

 large glands {rt. gl.), which have the same structure as the 

 spherical glands which I have recently described in the axis of 

 the gill of the adult Paljemonetes (No. 1). These glands 

 open by short ducts at the bases of the first maxillae, and they, 

 together with the smaller salivary glands {sal. gl), which are 

 present in considerable numbers in the upper lip, the parag- 

 naths, and the maxillse, have a great affinity for haematoxylin, 

 and assume a much brighter tint when that stain is used than 

 the surrounding tissues. 



The Dorsal Sac — I have found the dorsal sac in Palaemon 

 serratus, Palsemonetes varians,and Crangon vulgaris, 

 and in the adult it attains a considerable size. If a dissection 

 be made of an adult Palsemon the sac is readily seen (fig. 10). 

 Anteriorly it appears as a long cylindrical tube (c.) lying upon 

 the dorsal enlargement of the bladder (bl.), and containing 

 within it the cephalic aorta {Ao. c). Posteriorly it is very 



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