430 MEMOIRS OF THE NATIONAL ACADEMY CF SCIENCES. 



Ishikiiwa (27) fluds iu Atyephyra after the close of the iuvagiuatiou stage, certain proto- 

 plasmic eleiueuts uuder the ectoblast, which he thinks may correspoud with the " white yolk cle- 

 lueuts" just referred to, aud he also ideutifles-" secondary mesoderm cells," but does not trace 

 their origin or function. ' They are " small granules," easily stained by logwood solutiou, and some 

 are of considerable size and have a clear cell outline. "These are mostly aggregated in the 

 cephalic regiou between the involutions of the ectoderm cells, but are also found in all places." In 

 time of appearance aud in their position, he says they seem to correspond to the " secondary meso- 

 dei-m cells" of Astacus. This short uotice with his figures leaves little doubt that these bodies are 

 similar to those just described iu Alpheus and Homarus. Fig. 62 of his paper represents a longitu- 

 dinal median section of the egg nauplius, and may be compared with the same stage of Alpheus 

 (Figs. 104, 105), with respect to the general character and appearance of the degenerating cells. 



I have noticed similar nuclear fragments in the egg-nauplius of a crab (Fig. 113, PI. xl), aud 

 Lebedinski (34) has described "secondary mesoderm" in the embryo of the Mediterranean sea 

 crab, Eriphia spinifrons. According to this observer they are found in all stages from the " gastrula" 

 on, to the egg-nauplius; they are derived from ectoderm, and i«-obably give rise to blood cells. 

 In the stage with one pair of maxillipeds these elements are in active proliferation : 



Mau findet, die Zellen desselben bieten verschiedene Momente uud Zastande des Zerfalleas <lar; dieses Zerfallen 

 der Zellon stoht iu geuauen Zusammenhiinge mit der Entstehung der Blutliorper. 



He further says : 

 Ueber die Bildung des Blutes kann ich nlchts bestimintee mittheilen. Im Stadium des ersteu Paars kieferfussoheu 

 siud die ersten Blutkiirperclien vorhaudun, welche zuni ersteu Mai im Beroiche des Herzens vorkommen, wo sich auch 

 am friiliesten das sekuudiiro Mesoderm riickzubilden beginnt. 



From these quotations it appears that the " secondary mesoderm " shows signs of degenera- 

 tion, and its conversion into blood cells is an unverified inference. It seems more probable that 

 the structures iu question correspond with similar bodies already noticed iu Alpheus, Homarus, 

 and other Decapods, aud that in all cases they have to do primarily with the dissolution aud uot 

 with the construction of cells. 



Wheeler (07) iu his careful paper on the development of the Cockroach and Potato beetle 

 (Blatta germanica and Doryphora decemlineata) describes an interesting case of the decomposition 

 of nuclei, which bears a close analogy to what takes place in Alpheus and probaldy also in 

 Astacus. In Doryphora two masses of endoderm are found, one uuder the stomod;eum the other 

 under the caudal plate. At both these places numerous cells which originate in the endoderm 

 pass into the adjacent yolk and disappear. The process of dissolution is described as follows : 



Tile karyochylema becomes vacuolated, probably with substances absorbed from without, to judge of the larger 

 size of some of these nuclei, while the chromatin ceases to present the threadlike coil .aud becomes compacted into 

 irregular masses between the vacuoles. Finally the vacuoles fuse and the masses of cliromatiu, formally numerous, 

 agglomerate to form one or two large irregular masses which usually apply themselves to the wall of the clearly vesic- 

 ular nucleus * " * In the last stages seen the masses of chromatin lie between the yolk bodies, all other portions 

 of the nucleus having disappeared. They still take the deep red stain, but finally become comminuted .and disappear 

 in the intervitelline protoplasm. 



The vesiculated elements recall similar bodies which appear iu Keichenbach's plates. Thus 

 the element t, Fig. 88 of Wheeler's paper, where the chromatin is applied to the walls of the 

 nucleus, strikingly resembles nucleus i, Fig. 20 (see this paper), where the chromatin is similarly 

 disposed around the wall of a vacuole. 



Bruce (10) figures certain yolk cells undergoing what he considered to be endogenous cell 

 division iu an advanced embryo of a spider, aud compared it with the endogenous cell division 

 which Ileicheubach describes as taking place iu the endoderm cells of Astacus. 



The disintegration which has been attributed to the leucocytes of the mammalian blood 

 affords an interestiug comparison with the phenomena which have been described for the Arthropod 

 embryo. Howell's careful observations (25) support the view that the multiuucleated leucocytes 

 are disintegrating cells. " The leucoblasts enter the lymph stream, and eventually reach the 

 blood as unicellular leucocytes." Here they undergo changes, acquire amoeboid movements, while 

 the nuclei elongate, become constricted, and finally fragmented. " The nuilti nuclear stage * * » 

 is probably followed by a complete dissolution of the cell." Howell adopts the highly reasonable 



