108 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



produce a new cuticle wliich has a certain degree of elasticity. My material was insuf 

 ficient to trace with certainty the origin of the reticulated tissue which soon appears 

 under the new skin. 



A minute papilla grows out, having the general structure shown in fig. 173. It is 

 a spongy network of fibers, containing the potential elements of muscles, nerves, con- 

 nective tissue, and blood vessels. Blood flows in an irregular system of large and 

 small sinuses. The epidermis of the new skin, which is relatively much thinner than 

 the old, is composed of a single stratum of very tall, slender cells, the chitinogenous 

 epithelium, and of an elastic cuticula. The epidermis of the papilla is thus structurally 

 similar to that which covers all parts of the body when a new shell is being formed 

 under the old. (See p. 77.) 



As the papilla grows out the fibrous tissue becomes gradually differentiated into 

 the muscles, blood vessels, and nerves (fig. 172), as in an embryo, and constrictions in the 

 cuticle arise, which mark with absolute precision the limitation of the future joints. 

 The cuticle at this stage appears to be destitute of hairs, but it contains pores. In 

 the stump at the base of the appendage a great mass of large oval bodies is seen. 

 These appear as thin solid discs, and when compressed break like starch grains (fig. 

 121, pi. 36). They represent connective tissue cells in a certain stage of metamorphosis, 

 and in all probability contain glycogen, which furnishes material for the growth of the 

 epidermis — that is, of the chitinogenous cells and the shell which they secrete. (See 

 p. 78.) They seem to be the same structures which Leydig has described in the 

 integument of crabs, under the name of lime concretions (Kalkconcremente), and 

 which Hoeck calls "Krystall Plattchen" {121-122). Mayer (137) has also figured and 

 described what are probably similar bodies in the indurated shell of certain swellings 

 which are found in the large claws of the male Heterograpsus lucasii. These he desig- 

 nates as " amyl-like chitinous inclusions." 



In the lobster these bodies stain very diffusely, and sometimes a central figure, 

 possibly the impression or remains of the original nucleus, m ay be detected. The 

 histogenesis of these structures and the changes which they undergo have apparently 

 never been studied. Their origin is clearly demonstrated by fig. 122, plate 36, from 

 a preparation of the maxilliped. It is evident that the large granular mass is the 

 product of the parent mesoblastic cell, the protoplasm of which is reduced to a thin 

 enveloping shell. 



Fig. 169 represents one of a series of sections cut in a longitudinal plane through 

 the first three joints of the right large cheliped of the lobster (sixth stage, length 18 

 mm.), the history of which has been already given (p. 105). The appendage of this 

 larva had been cut off July 28, and had grown to nearly its full size by August 17, 

 when the animal was preserved. Since autotomy occurs in the very young animal as 

 well as in the adult, we should be able to determine from this specimen whether 

 there is any preformed organ or store of embryonic cells for the supply of the new 

 limb at this time. The examination of serial sections through this part of the limb 

 reveals nothing but normal tissue cells. Embryonic cells may be present but are 

 not discernible. The opening between the basipodite and ischiopodite is reduced to 

 a narrow passage by the ingrowth of cuticular cells, to form ectodermic pillars like 

 those seen in the carapace of the embryo. The several tissues are bathed in blood, 

 which is here confined to no definite channels. Some circumscription of the passage 

 leading from the second to the third joint is thus necessary. 



