CHAP. VIII. DEVELOPMENT OF ISOPODA. 71 



To the question, how far the development of Ligia 

 is repeated in the other Isopoda, I can only give an 

 unsatisfactory answer. The curvature of the embryo 

 upwards instead of downwards was met with by me as 

 well as by Eathke in Idothea, and likewise in Cassidina, 

 Philoscia, Tanais, and the Bopyridse, indeed, I failed 

 to find it in none of the Isopoda examined for this 

 purpose. In Cassidina also the first larval skin without 

 appendages is easily detected; it is destitute of the long 

 tail, but is strongly bent in the egg, as in Ligia, and 

 consequently cannot be mistaken for an "inner egg- 

 membrane." This, however, might 

 happen in Philoscia, in which the 

 larval skin is closely applied to the 

 egg-membrane (fig. 38), and is only 

 to be explained as the larval skin by 

 a reference to Ligia and Cassidina. F jg. 38< 3 

 The foliaceous appendage on the back 

 has long been known in the young of the common Water 

 Slater (Asellus)* That the last pair of feet of the thorax 



3 Fig. 38. Embryo of a Philoscia in the egg, magn. 25 diam. 



4 Leydig has compared this foliaceous appendage of the Water Slaters 

 with the " green gland " or " shell-gland " of other Crustacea, assuming 

 that the green gland has no efferent duct and appealing to the fact 

 that the two organs occur " in the same place." This interpretation is 

 by no means a happy one. In the first place we may easily ascertain 

 in Leucifer, as was also found to be the case by Glaus, that the " green 

 gland" really opens at the end of the process described by Milne- 

 Edwards as a " tubercule auditif" and by Spence Bate as an 

 " olfactory denticle." And, secondly, the position is about as dif- 

 ferent as it can well be. In the one case a paired gland, opening 

 at the base of the posterior antennae, and therefore on the lower 

 surface of the second segment ; in the other an unpaired structure rising 



