waite: antenxal glands in homarus americaxus. 189 



la this stage, the vessels and blood spaces (lac. sng.) which lie between 

 the eudsac and the ectodermic sac are for the first time seen to be 

 lined with endothelial cells. This vascular tissue has arisen from the 

 cells which are between the endsac and the ectodermic invagination, and 

 which are seen at later embryonic stages (Plate 3, Fig. 30) as attenu- 

 ated cells forming a sort of sheath around the endsac. 



In the fourth larva, the evaginations from the ectodermic sac have 

 further increased in number; those which occupy the positions of the 

 ones found in the third larva have elongated, and in some cases the free 

 end is folded back upon itself. On the doi-sal face of the ectodermic sac, 

 well forward, there is an evagination which is larger and more rounded 

 than the others. It contains a large cavity which is connected with the 

 main cavitv of the ectodermic sac bv a narrow duct. This evatrination 

 is directed backward and doraad ; it is the Jirst differentiation of the 

 vesicle of the adult gland. 



The globular vesicles on the free ends of the cells in the wall of the 

 ectodermic sac are more marked, and appear very much like the con- 

 dition in the adult. 



My material of the older larval stages is meagre and not in good his- 

 tological condition. It is difficult, in the absence of data as to the num- 

 ber of moults passed, to determine to what larval stage a given specimen 

 belongs. The sole criterion available is therefore that of length. 



In larvce IJf millimetres long, the dorsal rounded evagination represent- 

 ing the vesicle has increased much in size, extending caudad and dor- 

 sad, until its walls are in contact with those of the masticatory stomach. 

 The narrow slender evaginations have increased in number, especially in 

 the ventral part of the organ, and are so entangled that it is futile to at- 

 tempt to follow details. 



Larvce 18 millimetres long are the oldest tliat I have. According to 

 Herrick ('95, Table 3-4), this length indicates the seventh larval stage, 

 and life at the bottom of the sea. In these larvae the vesicle has enlarged 

 still more, its walls becoming thinner, until it covers dorsally nearly all 

 the organ. The complication of the slender evaginations is now still 

 greater, and anastomoses between adjacent evaginations are established 

 at many points by a breaking through of their walls. This condition is 

 found sparingly in the fourth larva, but in this (seventh V) stage it is 

 quite common. 



I have no material of adolescent stages in which to follow this process, 

 but there seems every reason to believe that it is by these evaginations, 

 with subsequent anastomoses, tliat the complication of tubules in the 



